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26 Sebaceous Carcinoma

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Fig. 26.5 Sebaceous carcinoma. Sebaceous carcinoma cells surrounding a hair follicle (arrow) indicating Zeis gland origin. Frozen 200× (Copyrighted by Steven N. Snow. Used with permission)

Sebaceous carcinoma is grouped into welldifferentiated, moderately differentiated, and poorly differentiated tumors.

SC invades adjacent structures by three mechanisms: (1) direct invasion, (2) pagetoid spread, and (3) multicentric discontinuous spread. There is a concern of “skip” areas.

Certain clinicopathologic features predict a poor prognosis and metastasis.

40% of the cases and mimics the normal sebaceous gland architecture with less differentiated cells at the periphery and more differentiated cells together with the accumulation of lipids centrally. About 32% display the comedocarcinoma pattern with lobules and large central necrosis surrounded by viable peripheral cells (Fig. 26.6) [34]. The papillary type shows papillary projections and sebaceous differentiation. The mixed pattern shows combinations of the three types. Basal cell carcinoma with sebaceous differentiation is negative for EMA and pagetoid spread, but has peripheral palisading of basal cells and clefting [35].

26.4Histopathology

SC is classified by pattern of differentiation, degree of differentiation, and mechanism of invasion [4].

26.4.1 Pattern of Differentiation

There are four classic invasive architectural patterns: (1) lobular, (2) comedocarcinoma, (3) papillary, and (4) mixed. Lobular pattern is observed in

26.4.2 Degree of Differentiation

Sebaceous carcinoma is grouped into well-differentiated, moderately differentiated, and poorly differentiated tumors. Well differentiated shows cells that resemble well developed lobular pattern. The atypical sebocytes possess large atypical nuclei that contain foamy cytoplasm. Moderate well-differentiated SC still shows a recognizable lobular pattern and frothy sebocytes [4]. In poorly differentiated SC, the lobular