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J. R. T. Monson and R. Hoedema
invasive colorectal carcinoma: a Japanese collaborative study. J Gastroenterol. 2004;39:534–43.
20. Kudo S.Endoscopic mucosal resection of at and depressed types of early colorectal cancer. Endoscopy. 1993;25:455–61.
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28. Bosch SL, Teerenstra S, de Wilt JH, Cunningham C, et al. Predicting lymph node metastasis in pT1 colorectal cancer: a sys­tematic review of risk factors providing rationale for therapy deci­sions. Endoscopy. 2013;45(10):827–34.
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31. Masaki T, Sugiyama M, Atomi Y, Matsuoka H, et al. The indi­cation of local excision for T2 rectal carcinomas. Am J Surg. 2001;181(2):133–7.
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2016. Mod Pathol. 2017;30(9):1299–311.
34. Sebag-Monteore D, Stephens RJ, Steele R, Monson J, et al. Preoperative radiotherapy versus selective postoperative chemo­radiotherapy in patients with rectal cancer (MRC CR07 and NCIC-CTG C016): a multicenter, randomized trial. Lancet. 2009;373:811–20.
35. Scheele J, Lemke J, Meier M, Sander S, et al. Quality of life after sphincter-preserving rectal cancer resection. Clin Colorectal Cancer. 2015;14:33–40.
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38. Garcia-Aguilar J, Mellgren A, Sirivongs P, Buie D, et al. Local excision of rectal cancer without adjuvant therapy: a word of cau­tion. Ann Surg. 2000;231:245–51.
39. Gopaul D, Belliveau P, Vuong T, Trudel J, etal. Outcome of local excision of rectal carcinoma. Dis Colon Rectum. 2004;47:1780–8.
40. Lawrence L, Kelly J, Nassif G, Atallah S, etal. Chemoradiation and local excision for T2N0 rectal cancer offers equivalent overall survival compared to standard resection: a national cancer database analysis. J Gastrointest Surg. 2017;21:1666–74.
41. Melnitchouk N, Fields A, Lu P, Scully RE, etal. Local versus radi­cal excision of early distal rectal cancers: a national cancer database analysis. Ann Surg Oncol. 2020;27(7):2169–76.
42. Albert MR, Atallah SB, de Beche-Adams TC, Izfar S, et al. Transanal minimally invasive surgery (TAMIS) for local excision of benign neoplasms and early-stage rectal cancer: efcacy and out­comes in the rst 50 patients. Dis Colon Rectum. 2013;56(3):301–7.
43. You N.Local excision: is it an adequate substitute for radical resec­tion in T1/T2 patients? Semin Radiat Oncol. 2011;21(3):178–84.
44. O’Neill CH, Platz J, Moore JS, Callas PW, etal. Transanal endo­scopic microsurgery for early rectal cancer: a single-center experi­ence. Dis Colon Rectum. 2017;60(2):152–60.
45. Ramirez JM, Aquilella V, Arribas D, Martinez M.Transanal full­thickness excision of rectal tumours: should the defect be sutured? A randomized controlled trial. Color Dis. 2002;4(1):51–5.
46. Brown C, Raval MJ, Phang PT, Karimuddin AA. The surgical defect after transanal endoscopic microsurgery: open versus closed management. Surg Endosc. 2017;31(3):1078–82.
47. Noura S, Ohue M, Miyoshi N, Yasui M. Signicance of defect closure following transanal local full-thickness excision of rectal malignant tumors. Mol Clin Oncol. 2016;5(4):449–54.
48. Hahnloser D, Cantero R, Salqado G, Dindo D, etal. Transanal min­imal invasive surgery for rectal lesions: should the defect be closed? Color Dis. 2015;17(5):397–402.
49. Lee L, Althoff A, Edwards K, Albert MR, Atallah SB, et al. Outcomes of closed versus open defects after local excision of rec­tal neoplasms: a multi-institutional matched analysis. Dis Colon Rectum. 2018;61(2):172–8.
50. Greenberg JA, Shibata D, Herndon JE, Steele GD, etal. Local exci­sion of distal rectal cancer: an update of cancer and leukemia group B 8984. Dis Colon Rectum. 2008;51(8):1185–91.
51. Bach SP, Hill J, Monson JR, et al. A predictive model for local recurrence after transanal endoscopic microsurgery for rectal can­cer. Br J Surg. 2009;96:280–90.
52. Junginger T, Goenner U, Hitzler M, etal. Long-term oncologic out­come after transanal endoscopic microsurgery for rectal carcinoma. Dis Colon Rectum. 2016;59:8–15.
53. Mellgren A, Sirivongs P, Rothenberger DA, et al. Is local exci­sion adequate therapy for early rectal cancer? Dis Colon Rectum. 2000;47:1773–9.
54. Stitzenberg KB, Sanoff HK, Penn DC, Meyers MO, Tepper JE.Practice patterns and long-term survival for early-stage rectal cancer. J Clin Oncol. 2013;31:4276–82.
55. Borstlap WA, Coeymans TJ, Tanis PJ, et al. Meta-analysis of oncological outcomes after local excision of pT1–2 rectal cancer requiring adjuvant (chemo)radiotherapy or completion surgery: oncological outcomes after local excision of rectal cancer. Br J Surg. 2016;103:1105–16.
56. Cutting JE, Hallam SE, Thomas MG, Messenger DE.A systematic review of local excision followed by adjuvant therapy in early rectal cancer: are pT1 tumors the limit? Color Dis. 2018;20:854–63.
57. Kapiteijn E, Marijnen CA, Nagtegaal ID, et al., on behalf of the Dutch Colorectal Cancer Group. Preoperative radiotherapy com­bined with total mesorectal excision for resectable rectal cancer. N Engl J Med. 2001;345:638–46.
58. Sauer R, Becker H, Hohenberger W et al., on behalf of the German Rectal Cancer Study Group. Preoperative versus post­operative chemoradiotherapy for rectal cancer. N Engl J Med. 2004;351:1731–40.
59. Habr-Gama A, Perez RO, Nadalin W, etal. Operative versus nonop­erative treatment for stage 0 distal rectal cancer following chemora­diation therapy. Ann Surg. 2004;240:711–7.
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Rectal Cancer: Nonoperative Management

JulioGarcia-Aguilar andRodrigoOlivaPerez
28
Key Concepts
• A proportion of patients with rectal cancer managed by neoadjuvant chemoradiation may achieve complete dis­appearance of the primary tumor (complete clinical response) during assessment of response after treatment completion.
• Establishing a complete clinical response requires the combination of clinical, endoscopic, and radiological ndings consistent with the absence of residual cancer at the site of the original cancer.
• Patients that achieve a complete clinical response have been considered for organ preservation strategy with strict surveillance and no immediate surgery (Watch and Wait) to avoid the potential morbidity, mortality, requirement for stomas, and functional consequences of a proctectomy.
• Patients that achieve a complete clinical response and are managed by the Watch and Wait strategy have a 25% risk for developing local regrowth of the primary tumor.
• The majority of local regrowths are amenable to successful salvage proctectomy with negative resection margins (R0).
• Patients that achieve a cCR and are managed by Watch and Wait have similar overall survival rates when com­pared to patients with pCR managed by radical proctec­tomy. Disease-free survival rates are superior for patients undergoing radical proctectomy due to the 25% risk of
Supplementary Information The online version of this chapter (https://doi.org/10.1007/978- 3- 030- 66049- 9_28) contains supplemen­tary material, which is available to authorized users.
J. Garcia-Aguilar (*) Department of Surgery, Memorial Sloan Kettering Cancer Center, New York, NY, USA e-mail: garciaaj@mskcc.org
R. O. Perez Department of Surgical Oncology, Angelita and Joaquim Gama Institute, Benecencia Portuguesa de Sao Paolo, Alemao Oswaldo Cruz, Sao Paulo, Brazil
local regrowth following WW requiring salvage proctectomy.
• Functional outcomes and quality of life appear to be improved among patients with complete clinical response managed by Watch and Wait when compared to proctectomy.

Introduction

The introduction of neoadjuvant therapy has led to signi­cant changes in the management of rectal cancer. The obser­vation of a variable degree of tumor response to neoadjuvant therapy has challenged the previously standard practice of proctectomy and has prompted the introduction of new treat­ment algorithms. The assessment of tumor response after neoadjuvant therapy, previously considered unnecessary, is now an integral part of contemporary rectal cancer manage­ment algorithms. Patients found to have clinical, endoscopic, and radiological evidence of complete disappearance of the primary tumor are considered candidates for deferral of sur­gery and active surveillance, with the ultimate goal of achiev­ing sustained organ preservation, a strategy known as Watch and Wait (WW). In this chapter we will review rectal cancer management with an emphasis on baseline staging, neoadju­vant treatment regimens, timing and methods for assessment of tumor response, and surveillance protocols relevant for the effective and safe implementation of WW strategies that will result in optimal organ preservation. We will also pro­vide an overview of the evidence supporting the WW strat­egy for rectal cancer patients who achieve a clinical complete response to neoadjuvant therapy.
Terminology andDenitions
Organ preservation strategies in the management of rectal cancer require new terms and denitions.
© Springer Nature Switzerland AG 2022 S. R. Steele et al. (eds.), The ASCRS Textbook of Colon and Rectal Surgery, https://doi.org/10.1007/978-3-030-66049-9_28
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The nal histologic stage of the tumor after neoadjuvant therapy should follow the nomenclature of the AJCC/IUCC TNM classication [1]. ypT0 indicates no residual tumor in the bowel wall in the primary tumor bed (within the rectal wall), whereas ypN0 means negative nodes in the mesorec­tum when part of the surgical specimen. The term pathologic complete response (pCR) should be reserved for ypT0N0 tumors in patients who had a proctectomy or for ypT0 tumors after a full-thickness local excision (LE) without radiologi­cal evidence of mesorectal positive nodes or deposits.
Patients without evidence of tumor on clinical, endo­scopic, and radiological exams are considered to have a clin­ical complete response (cCR) [2]. The key to determining whether a WW strategy will likely be successful is based on the assumption that cCR after neoadjuvant therapy correlates with pCR after proctectomy [3].
The goal of the WW strategy is to identify patients who have no residual disease in the bowel wall after neoadjuvant therapy who can avoid surgery and preserve the rectum [4]. Therefore, the term Watch and Wait was originally used exclusively for patients who achieved a cCR and were offered no immediate surgery with strict and close surveillance [4]. This means that achieving a cCR is a prerequisite for enter­ing a WW program.
Considering the lack of a “perfect” correlation between cCR and pCR, some patients with a cCR entering a WW program are at risk of local regrowth during follow-up [5]. The reappearance of the tumor in the rectal wall or in the regional lymph nodes after an apparent cCR is called local regrowth [6]. Regrowths occur more often in the bowel wall compared to the regional lymph nodes and therefore are more easily detected by digital rectal examination (DRE) and/or exible sigmoidoscopy. Most local regrowths are potentially salvageable by surgery [712]. Any tumor reap­pearance in the pelvis after a curative-intent surgery is con­sidered “local recurrence.” Distant metastases can occur in patients with a sustained cCR but are more frequent in patients with tumor regrowth.
Historically, most rectal cancer patients entered in a WW protocol had received standard long-course chemora­diation therapy (CRT) [4, 12, 13]. As treatment strategies evolved over time, systemic chemotherapy was progres­sively added to standard neoadjuvant CRT regimens. Chemotherapy that is given before CRT is called induction chemotherapy, and chemotherapy given during and after CRT (before surgery) is called consolidation chemotherapy [1417]. The full regimen of induction or consolidation chemotherapy (eight cycles of FOLFOX [leucovorin, uo­rouracil, oxaliplatin] or ve cycles of CapeOX [capecitabine, oxaliplatin]) in combination with CRT is called total neo- adjuvant therapy [18].
Radiation therapy delivery has also evolved over time. Originally, most treatment regimens included external beam radiotherapy (EBRT), with or without intensity modulation
techniques (IMRT). In addition to the mode of delivery, frac­tionation of doses may encompass two different regimens: long-course with hyperfractionation or short-course with hypofractionation. Even though a detailed description of these different approaches is beyond the scope of this chap­ter, sufce to say that both regimens may result in pCR and/ or cCR [19, 20]. In an attempt to increase the total dose of radiation delivery, techniques have been developed to pro­vide maximal dose (dose escalation) with minimal toxicity. Therefore, additional doses (boosts) to the primary tumor may be delivered by EBRT, endorectal high-dose-rate brachytherapy (HDBRT) or contact radiation (Papillon tech­nique) [16, 17, 21, 22].

Rationale

The possibility of a permanent stoma has always been one of the main concerns of patients diagnosed with rectal cancer. Even though patients’ perspectives may vary across different geographical areas and cultures, a permanent end-colostomy impacts body image and impairs quality of life [23]. The concept of avoiding surgery in rectal cancer patients treated with neoadjuvant chemoradiation was driven by the observa­tion of pCR in patients treated with abdominal-perineal resection (APR) with permanent colostomy [4]. Following similar observations from anal cancer treatment, where patients with complete tumor regression after neoadjuvant chemoradiation (nCRT) avoided radical surgery with sur­prisingly favorable oncological outcomes, initial attempts were made to identify rectal cancer patients who had achieved a pCR, by means of clinical, endoscopic, and radio­logical examination [24]. However, most rectal cancer patients have more surgical options than anal cancer patients, for whom APR is the main radical surgical alternative. Depending on tumor stage, anatomy, and relation to the anal sphincter complex, many rectal cancer patients are candi­dates for sphincter preserving procedures. Although avoid­ing a permanent stoma, restorative proctectomy is often associated with signicant bowel dysfunction, particularly worsened by previous exposure to ionizing radiation to the pelvis. A sizeable fraction of patients who undergo a restor­ative procedure with their temporary diverting stoma reversed are left with variable degrees of fecal incontinence and a constellation of symptoms known as “low anterior resection syndrome,” some requiring conversion to a permanent stoma or creation of cecostomy/appendicostomy for anterograde colon lavage [2527]. In addition, proctectomy, with or with­out sphincter preservation, has signicant consequences in terms of sexual and urinary function [28, 29].
Despite recent advances in minimally invasive approaches to the surgical management of rectal cancer, proctectomy is also associated with immediate postoperative morbidity and mortality [30]. One of the main drivers of postoperative mor-
28 Rectal Cancer: Nonoperative Management
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bidity among these patients is the risk of postoperative anas­tomotic leak. Prospective randomized clinical trials have shown the benets of diverting stomas in decreasing the risk of clinically relevant leaks and the need for urgent reopera­tions among these patients [31]. However, the creation of a diverting stoma often results in direct morbidity associated with high-output syndromes (with ileostomy) and with sub­sequent stoma reversal [32]. Altogether, avoidance of potentially unnecessary proctectomy among patients with complete tumor regression after nCRT could have the poten­tial benets of sparing patients from the need of a permanent or temporary stoma, risk of immediate and late morbidity, chance of postoperative mortality, and negative functional consequences in bowel, urinary, and sexual functions [30
35]. In addition, patients undergoing proctectomy for rectal
cancer will have potentially signicant long-term nancial and social burdens beyond the clinical aspects of the disease and its treatment. These patients will need resources to nance surgical treatment as well as its potential complica­tions, the cost of supplies for the stoma, and assistance deal­ing with the impact of proctectomy on the activities of daily living and professional life [36].
Primary Tumor Assessment andSelection Criteria
Baseline tumor assessment for patients being considered for organ preservation is of paramount importance and is based primarily on clinical ndings of DRE, endoscopic features, and radiological imaging. Neoadjuvant therapy should only be instituted after these studies are complete, and conrma­tory biopsies of adenocarcinoma have been obtained and properly documented.
Accidental Versus Intentional WW
The occasional eradication of rectal cancer by radiation ther­apy has been known for decades. Attempts to cure rectal can­cer with radiation alone were popular at the beginning of the twentieth century, when the mortality and morbidity of rectal cancer surgery were prohibitive [37]. The difculty in iden­tifying patients with a true complete response and increased safety of surgery ultimately led to the abandonment of the idea of treating cancer with radiation alone. Over the years, some surgeons have omitted surgery in some patients with an apparent complete or near-complete response because of advanced age, high surgical risk from comorbid conditions, or patient refusal of a permanent stoma. This “accidental” approach to WW, still the only one accepted at many institu­tions, should be distinguished from the systematic or “inten­tional” approach, in which patients with distal rectal cancer likely requiring restorative proctectomy with low colorectal
anastomosis or non-restorative proctectomy with permanent colostomy are treated with optimal neoadjuvant therapy, restaged, and selectively entered in a WW protocol with the intention of achieving permanent organ preservation [38]. Chances of achieving a cCR are now anticipated, and consid­eration of WW is discussed prior to treatment with nCRT.The intentional WW approach is relatively straightforward in patients with locally advanced rectal cancer requiring nCRT before proctectomy for oncological purposes. However, patients with less advanced disease, not necessarily requiring nCRT before proctectomy for oncological reasons, may also be considered for WW and undergo nCRT for the primary purpose of achieving a cCR [38].
Baseline Stage
Baseline tumor stage is an important predictor of tumor response to nCRT.In general, more advanced tumors are less likely to completely respond to nCRT compared to early­stage tumors. Therefore, clinical stage has potential implica­tions for the selection of patients for WW.Current guidelines recommend nCRT for patients with locally advanced tumors that have baseline features indicative of high risk of local recurrence following proctectomy alone [39]. A distance of the primary tumor to the mesorectal fascia of ≤1 mm (mrCRM1mm including T3c,d or T4), extramural venous invasion (EMVI), extensive nodal disease (N1c/N2), or lat­eral pelvic sidewall nodes (LPNM) have been associated with the risk of local recurrence after proctectomy alone and therefore are currently indications for nCRT.While the pres­ence of these features is not a contraindication for WW, a cCR is less likely in patients with such advanced tumors. In addition, clinical and radiological identication of a cCR may be quite challenging in the presence of extensive dis­ease, where it may be difcult to ascertain whether palpable or radiographic extraluminal abnormalities are due to brotic changes versus remaining tumor following neoadjuvant therapy.
The indication for nCRT in patients with intermediate dis­ease—those with mrT3a,b or N0/1 and no additional high­risk features (CRM1 mm, EMVI+, LPNM+)—is controversial. While such patients are still considered candi­dates for nCRT in international guidelines that use the TNM classication system as the basis for risk stratication (such as the guidelines of the National Comprehensive Cancer Network; www.nccn.org), data from the MERCURY trial suggest that these patients are at low risk for local recurrence after proctectomy, casting doubt on the need for nCRT [40]. While the debate about the benets of nCRT for all intermediate- risk rectal cancer patients is beyond the scope of this chapter, offering nCRT to patients with more distal intermediate stage tumors offers the possibility of a cCR and potential organ preservation [41].
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A similar treatment algorithm may be considered for patients with early-stage disease (mrT1/T2N0). As the local recurrence rate with proctectomy alone is very low, early­stage tumors are typically not considered candidates for nCRT.However, nCRT followed by local excision has been proposed as an alternative for patients with early-stage distal rectal cancer who otherwise would need a coloanal anasto­mosis or a permanent colostomy. Several phase II trials have shown that the rate of pCR for these patients is higher than in patients with more advanced disease [3, 42]. It is therefore reasonable to offer WW to patients with early-stage rectal cancer who seek to avoid a permanent stoma and start treat­ment with nCRT in an attempt to achieve a cCR.
Tumor Location
Tumor location is also important when selecting patients for WW.While any rectal cancer patient with a cCR after CRT is a potential candidate for WW, those more likely to benet from a WW approach that may result in organ preservation are patients with tumor located in the distal rectum who may otherwise need a low colorectal or coloanal anastomosis or a permanent colostomy. Tumors in this location are also more likely to be accessible to monitoring by DRE [2].
Tumor location in the distal rectum is particularly impor­tant when considering nCRT with the goal of achieving cCR in early-stage tumors. mrT2 cancers beyond the reach of DRE are probably surrounded by mesorectal fat and are less likely to have CRM positivity and local recurrence if treated by up-front proctectomy. As most of these patients are candi­dates for sphincter-saving surgery, they are less likely to ben­et from organ preservation. However, an exception to this rule is an obese patient with a long anal canal in whom a tumor located immediately above the anorectal ring may be just beyond the reach by DRE but who may still be a candi­date for a WW strategy.
Magnetic resonance imaging using dedicated rectal can­cer protocols provides valuable information about the loca­tion of the tumor in relation to other anatomical structures, such as the sphincter complex, the levator muscles, the pros­tate and seminal vesicles, the vaginal wall and cervix, as well as the anterior peritoneal reection and helps the surgeon anticipate the need for a permanent stoma, the ability to per­form a sphincter-saving procedure and even the type of anas­tomosis in case proctectomy is undertaken. This information is also very useful for the selection of patients for WW [43]. In summary, patients with lower tumors requiring a low colorectal or a hand-sewn coloanal anastomosis or an APR are more likely to benet from a WW strategy and organ preservation. Patients with more proximal tumors that carry
a low risk of local recurrence and unlikely to benet from CRT will derive minimal benet from organ preservation and may be better treated with up-front proctectomy.
Endoscopic Features
Some endoscopic features such as pit pattern and submuco­sal vascular architecture can help identify benign lesions or even supercially invasive rectal cancers that fulll the crite­ria for endoscopic submucosal resection (see Chap. 23) or transanal local excision (see Chap. 27) without the need for proctectomy or nCRT [44].
Endoscopic and some DRE features related to tumor mor­phology have not been associated with differences in response rates to neoadjuvant treatment. Therefore, qualities commonly associated with more advanced disease, such as ulceration and tethered lesions, are not necessarily exclusion criteria for entering WW. Size has been associated with response, suggesting that smaller tumors are more likely to respond completely to treatment [45]. Still, even patients with large circumferential tumors may also achieve a cCR and successfully undergo WW.Proper documentation of the endoscopic characteristics of the tumor at baseline—ideally through endoscopic images—is important for subsequent evaluations during the assessment of tumor response. Some large, circumferential, ulcerated tumors develop a concentric scar that narrows the lumen of the rectum and prevents proper endoscopic evaluation of tumor response. Patients with such tumors may not be ideal candidates for WW because complete endoscopic assessment and surveillance are not possible.
In summary, patients being considered for nCRT with the hope of entering a WW program should have conrmation of invasive adenocarcinoma, a tumor that is (preferably) acces­sible to DRE, endoscopic features consistent with invasive cancer not suitable for endoscopic submucosal dissection, and an MRI showing a tumor located in the distal rectum. Baseline staging features may be useful for estimating the probability of a tumor achieving a cCR and selecting a treat­ment plan that will potentially include a WW strategy to achieve organ preservation.
Assessment ofTumor Response
Most rectal cancers respond to some degree to chemotherapy and radiation. The degree of response depends on intrinsic tumor characteristics, such as size, stage, and some genomic features and treatment variables, including the fractionation dose of the radiation and the time from completion of radio-
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therapy to assessment of response. In a WW program, tumor response is assessed with the same diagnostic tools as for the initial staging: DRE, endoscopy, and radiology (preferably MRI).
The 6-week interval between the end of the neoadjuvant therapy and surgery in patients with stage II-III rectal cancer treated with CRT and proctectomy has been proven to be effective in terms of surgical technical difculty and periop­erative morbidity and is associated with a pCR rate of approximately 18% [46]. Retrospective studies have sug­gested that longer intervals between the end of radiotherapy and surgery result in higher pCR rates [47, 48]. These data, along with the growing body of evidence from patients entered in WW protocols, suggest that tumor response is time-dependent and probably nonlinear [4951]. These nd­ings have implications for the design of WW strategies: tumors that have responded signicantly but have not achieved a cCR at the time of the initial evaluation 6–8weeks after completion of CRT may still achieve a cCR with longer observation. Several prospective studies suggest that adding chemotherapy during the longer observation period increases the likelihood of cCR and the probability of organ preserva­tion [15, 18].
Our current WW strategy is to assess tumor response 6–8weeks after completion of neoadjuvant therapy. Based on the degree of tumor response, patients are stratied in one of three treatment groups (Table28.1) [52]. Patients with an incomplete clinical response (iCR) and a clearly visible tumor, even if the tumor has decreased in size signicantly from baseline, typically undergo surgery (Table 28.1, Fig. 28.1). Patients with a cCR can enter a standard WW surveillance protocol with repeat assessments every 3–4months (Table28.1, Fig.28.2). Patients with a very sig­nicant response that does not meet all criteria of a cCR— termed a near-complete clinical response (nCR)—can be entered in an intensive surveillance protocol, with a repeat
exam after 6–8 additional weeks (Table 28.1, Fig. 28.3). Continued observation at similar intervals may be appropri­ate as long as the tumor continues showing signs of ongoing response until all strict criteria of a cCR are achieved. Most patients should achieve all strict criteria within 28–34weeks following completion of radiotherapy. While not the norm, it may take up to a year (52weeks) for some tumors to achieve a cCR.A lack of evidence of continued response in any of the three diagnostic modalities or any sign of tumor regrowth is an indication for surgery.
Criteria foraComplete Clinical Response
The criteria of a complete clinical response are based on three pillars of assessment. Clinical evaluation with DRE should reveal a regular mucosal surface, with only minor induration of the rectal wall and no signicant abnormali­ties. Endoscopic assessment is typically characterized by whitening of the mucosa with telangiectasias and absence of ulceration, mass, or stenosis of the rectum (Figs. 28.4 and 28.5). Radiological assessment should include the presence of an area of low-signal intensity at the original tumor location on MRI-T2W [magnetic resonance tumor regression grade 1 (mrTRG1)] (Fig. 28.6); restriction to diffusion on MRI-DW should be absent, corresponding to the area of low-signal intensity on T2-weighted images (Fig.28.7).
Given the random distribution of cancer cells in the differ­ent layers in the rectal wall after nCRT [53, 54], endoscopic biopsies are not very useful in the assessment of rectal cancer response to CRT.A negative biopsy is not a requirement for patients with a cCR entering a WW protocol. Conversely, a negative endoscopic biopsy cannot exclude residual tumor in patients with near-complete or incomplete clinical response. Therefore, endoscopic biopsy in patients with an incomplete
Table 28.1 Clinical response and suggested management
Clinical response Endoscopic features Clinical features Radiological features (MR) Suggested management
Incomplete Deep ulcerations, elevated
Near­complete
Complete Only whitening of the
borders, signicant distortion of rectal wall
No visible mass, only supercial/shallow ulcer
mucosa and/or telangiectasias
Hard palpable mass, signicant stenosis
Minimal/ questionable irregularity
Smooth surface in DRE
mrTRG3-5, mixed or high-signal intensity, restriction to diffusion in the corresponding area of the primary tumor
mrTRG 2 Reassessment in 8–12weeks;
Low-signal intensity (T2-weighted images), absence of diffusion restriction (corresponding area), mrTRG1
Surgical management
further response should be documented in subsequent reassessment
WW, reassessment in 12weeks
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Fig. 28.1 Partial response (not near-complete). Endoscopic view of a rectal cancer at baseline (a) and exhibiting a clear large and necrotic residual ulcer (70% response) by endoscopy at 6weeks (b). Similar
response, for the purpose of convincing patients that they have residual cancer in the setting of incomplete clinical response, is risky because a negative biopsy may give the patient a false sense of security and an argument to refuse a recommended operation [55].
One of the challenges for broad implementation of WW is establishing uniform and reproducible criteria for tumor response. Each modality is accurate but imperfect. Combining modalities increases accuracy [56]. In their investigation of the accuracies of DRE, endoscopy, and MRI in predicting pCR or sustained cCR, Maas etal. found that
ndings can be seen in baseline MR showing a mrT3N0 (c, dotted yel­low line) and 70% response (mrTRG3, dotted yellow line) at 6weeks (d). Achievement of a cCR is unlikely
clinical assessment was the most accurate. When all three modalities were consistent with absence of residual tumor, the accuracy of predicting complete response was 98% [56]. A three-tiered response assessment schema currently being tested in the OPRA trial (organ preservation in rectal adeno­carcinoma) consists of DRE, endoscopy, and T2- and diffusion- weighted MRI [52]. Based on that assessment, patients are considered complete responders, incomplete responders, or near-complete responders. Studies aimed at validating the reproducibility of that response assessment schema are underway.
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c d
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b
Fig. 28.2 Near-complete response followed by cCR.Endoscopic view of a rectal canvcer at baseline (a) and exhibiting near-complete/major (>70%) response by endoscopy at 6weeks (b). Similar ndings can be seen in baseline MR showing a mrT2/T3aN0 (c) and >70% response
Endoscopic andClinical Assessment
Historically, the rst experiences of WW were reported prior to the development and standardization of radiological imaging in rectal cancer. Therefore, assessment of tumor response relied mostly on clinical (DRE) and endoscopic assessment [4].
DRE may seem like a simple and a rather straightforward tool for assessment of tumor response. However, DRE may be quite challenging for distinguishing between cCR and residual disease in many clinical scenarios. In this setting, it is recommended that the colorectal surgeons involved in organ-preserving programs be able to examine patients by DRE at baseline and during assessment of response. A DRE assessment of the baseline features of the primary tumor may
(mrTRG2) at 6weeks (d). Achievement of a cCR is more likely, and patients should be reassessed in 6–8-week intervals. Further reassess­ment of response at 16weeks showed cCR by endoscopy and MR
aid the interpretation of response to treatment. Usually, cCR should result in a smooth and regular mucosal surface of the rectum. Even though slight induration of the rectal wall may often be palpated, ulcerations, nodules, stenosis, and masses should always raise the suspicion for residual cancer, and patients with these characteristics are thought not to be appropriate candidates for WW [2].
Endoscopic assessment may be equally challenging. Even though rigid proctoscopy may sufce for the identication of a cCR with strict criteria (see above), exible endoscopy pro­vides additional benets in terms of improved visualization, more accurate documentation, training, and patient comfort. In addition, exible instruments may provide the opportunity for retroexion and more precise examination of the areas immediately adjacent to the dentate line. Finally, magnifying
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a
b
Fig. 28.3 Complete clinical response. Endoscopic view of a rectal cancer at baseline (a) and exhibiting strict criteria of cCR by endoscopy at 6weeks (b). Similar ndings can be seen in baseline MR showing a mrT2 (c, dotted yellow line) and mrTRG1 (d, dotted yellow line) at 6weeks
endoscopic features including narrowband imaging may pro­vide additional advantages during the assessment of tumor response after nCRT (Fig.28.8).
in baseline staging for rectal cancer and was also used for the assessment of tumor response to nCRT.This imaging modality provides good accuracy for the identication of complete response in the primary cancer (ypT status). However, patient discomfort and the difculties in assess-

Radiological Studies

ing mesorectal disease away from the rectal lumen contrib­uted to the replacement of ERUS by alternative radiological
Several radiological tools have been tested in clinical prac­tice for the assessment of tumor response to nCRT.Endorectal ultrasound (ERUS) was originally used
imaging modalities [57, 58].
Magnetic resonance is currently the imaging modality of
choice for baseline staging and assessment of response to