Case 5—A 66-year-old woman presented for evaluation of a posterior scalp mass measuring 23×18 mm that had grown over the last 24 months. Biopsy showed mucinous carcinoma with lymphovascular invasion consistent with PCMC (Figure 5) confirmed on multiple tissue levels and with the aid of immunohistochemistry. She was sent for an MRI of the head, neck, chest, abdomen, and pelvis, which demonstrated 2 enlarged postauricular lymph nodes and raised suspicion for metastatic disease vs reactive lymphadenopathy. Mohs micrographic surgery with frozen sections was performed with 1- to 3-mm margins; the final layer was sent for permanent processing and confirmed negative margins. Sentinel lymph node biopsy and lymphadenectomy of the 2 nodes present on imaging showed no evidence of metastasis. The patient had no recurrence in 1 month.
FIGURE 5. Histopathology revealed a primary cutaneous mucinous carcinoma with lymphovascular invasion (yellow arrow)(case 5) (H&E, original magnification ×20).
Comment
Endocrine mucin-producing sweat gland carcinoma and PCMC are sweat gland malignancies that carry low metastatic potential but are locally aggressive. Endocrine mucin-producing sweat gland carcinoma has a strong predilection for the periorbital region, especially the lower eyelids of older women.3 Primary cutaneous mucinous carcinoma may arise on the eyelids, scalp, axillae, and trunk and has been reported more often in older men. These slow-growing tumors appear as nonspecific nodules.3 Lesions frequently are asymptomatic but rarely may cause pruritus and bleeding. Histologically, EMPSGC appears as solid or cystic nodules of cells with a papillary, cribriform, or pseudopapillary appearance. Intracellular or extracellular mucin as well as malignant spread of tumor cells along pre-existing ductlike structures make it difficult to histologically distinguish EMPSGC from ductal carcinoma in situ.3
A key histopathologic feature of PCMC is basophilic epithelioid cell nests in mucinous lakes.4 Rosettelike structures are seen within solid areas of the tumor. Fibrous septae separate individual collections of mucin, creating a lobulated appearance. The histopathologic differential diagnosis of EMPSGC and PCMC is broad, including basal cell carcinoma, hidradenoma, hidradenocarcinoma, apocrine adenoma, and dermal duct tumor. Positive expression of at least 1 neuroendocrine marker (ie, synaptophysin, neuron-specific enolase, chromogranin) and low-molecular cytokeratin (cytokeratin 7, CAM5.2, Ber-EP4) can aid in the diagnosis of both EMPSGC and PCMC.4 The use of p63 immunostaining is beneficial in delineating adnexal neoplasms. Adnexal tumors that stain positively with p63 are more likely to be of primary cutaneous origin, whereas lack of p63 staining usually denotes a secondary metastatic process. However, p63 staining is less reliable when distinguishing primary and metastatic mucinous neoplasms. Metastatic mucinous carcinomas often stain positive with p63, while PCMC usually stains negative despite its primary cutaneous origin, decreasing the clinical utility of p63. The tumor may be identical to metastatic mucinous adenocarcinoma of the breast, gastrointestinal tract, lung, ovary, and pancreas. Tumor islands floating in mucin are identified in both primary cutaneous and metastatic disease to the skin.3,6 Areas of tumor necrosis, notable atypia, and perineural or lymphovascular invasion are infrequently reported in EMPSGC or PCMC, though lymphatic invasion was identified in case 5 presented herein.
A metastatic workup is warranted in all cases of PCMC, including a thorough history, review of systems, breast examination, and imaging. A workup may be considered in cases of EMPSGC depending on histologic features or clinical history.
There is uncertainty regarding the optimal management of these slow-growing yet locally destructive tumors.5 The incidence of local recurrence of PCMC after WLE with narrow margins of at least 1 cm can be as high as 30% to 40%, especially on the eyelid.4 There is no consensus on surgical care for either of these tumors.5 Because of the high recurrence rate and the predilection for the eyelid and face, MMS provides an excellent alternative to WLE for tissue preservation and meticulous margin control. We advocate for the use of the Mohs technique with permanent sectioning, which may delay the repair, but reviewing tissue with permanent fixation improves the quality and accuracy of the margin evaluation because these tumors often are infiltrative and difficult to delineate under frozen section processing. Permanent en face sectioning allows the laboratory to utilize the full array of immunohistochemical stains for these tumors, providing accurate and timely results.
Limitations to our retrospective uncontrolled study include missing or incomplete data points and short follow-up time. Additionally, there was no standardization to the margins removed with MMS or WLE because of the limited available data that comment on appropriate margins.