24.3Management of Merkel Cell Carcinoma

24.3.1 Patient Evaluation and Staging

Patient evaluation begins with assessment of the primary tumor and correct histopathologic diagnosis using hematoxylin and eosin as well as immunostains. Once the diagnosis of MCC is established, a complete skin and clinical lymph node exam is recommended to evaluate for regional and/or distant spread. If clinically indicated, imaging should be performed for staging purposes. Useful imaging modalities include computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography–computed tomography (PET-CT) [20].

Multiple competing staging systems have been proposed in the past [21–24]. Given the heterogeneity of these systems, the American Joint Committee on Cancer

(AJCC) developed Merkel cell-specific guidelines using the primary tumor, regional lymph node involvement, and distant metastasis (TNM system) [25]. In summary, stage I and II define patients with local disease based on tumor size (I is <2 cm; II is >2 cm). If patients are pathologically node-negative they are substaged as A (substaged as B if only clinical evaluation of nodes was performed). Patients with lymph node involvement are stage III (substaged as A for pathologically positive, clinically occult nodes and B for clinically evident nodes). Stage IV defines patients with distant metastasis [25].

Sentinel lymph node (SLN) evaluation has been advocated in the evaluation of patients with melanoma, and a similar approach has been proposed for MCC. Studies have shown MCC spreads in an orderly fashion, and metastasis occurs via lymphatic spread to regional lymph nodes prior to systemic spread [21].