To the Editor:
Primary mucinous carcinoma (PMC) is an exceedingly rare adnexal tumor with an incidence of 0.07 cases per million individuals.1,2 First described by Lennox et al3 in 1952, this entity often presents as slow-growing, solitary nodules that often are soft on palpation but may have an indurated quality and range in color from reddish blue to flesh colored to white.4 Primary mucinous carcinoma most commonly is found on the eyelid (38%) but may affect other sites on the face (20.3%), scalp (16%), and axilla (10%).5 Historically, it has been thought to be more common among men; however, a 2005 large case series by Kazakov et al5 found that women were twice as likely to be affected. Primary mucinous carcinoma most frequently is diagnosed in the fifth through seventh decades of life, with a median age at onset of 63 years.6,7 Because of its rarity, PMC is most frequently confused clinically with basal cell carcinoma, keratoacanthoma, apocrine hidrocystoma, epidermoid cyst, Kaposi sarcoma, neuroma, lacrimal sac tumor, squamous cell carcinoma, granulomatous tumors, and metastatic adenocarcinoma.1,8-10
Primary mucinous carcinoma is thought to be derived from sweat glands, and select features such as decapitation secretion are more suggestive of apocrine than eccrine differentiation.5,8 On histopathology, PMC classically is described as nests of epithelial cells floating in lakes of extracellular mucin, primarily in the dermis and subcutis. The nests are composed of basaloid cells in solid to cribriform arrangements, usually with a low mitotic count and little nuclear atypia. These nests are suspended within periodic acid–Schiff positive mucinous pools partitioned by delicate fibrous septa. The mucin produced by PMC is sialomucin, and as such it is hyaluronidase resistant and sialidase labile.6 At least 1 report has been made of the presence of psammoma bodies in PMC.11
The neoplasm is characterized by an indolent course with frequent recurrence but rare metastasis.5,12 Treatment is primarily surgical, with Mohs micrographic surgery (MMS) offering improved tissue conservation and reduced recurrence rates.12 The diagnostic challenge lies in distinguishing PMC from a variety of metastatic mucinous internal malignancies that portend a notably greater morbidity and mortality to the patient. We describe a case of PMC, discuss the differentiation of PMC from metastatic mucinous carcinoma, and review the literature regarding treatment of this rare neoplasm.
A 65-year-old white woman was referred to our tertiary-care dermatologic surgery clinic for treatment of an incompletely excised mucinous carcinoma of the right lateral canthus (Figure 1). The clinically evident scar measured 0.5×0.5 cm. Although difficult to appreciate in Figure 1, a slight textural change of the surrounding skin, including the upper and lower eyelid, was apparent. Prior to her arrival to our clinic, the referring physician had completed a thorough review of systems and physical examination, which did not suggest an underlying malignancy. Computed tomography of the head, neck, chest, abdomen, and pelvis revealed a mass in the thyroid that was removed and found to be benign. The patient’s cutaneous lesion was therefore considered to be a PMC of the skin.
Figure 1. Primary mucinous carcinoma of the right lateral canthus (clinical lesion within red circle) that was incompletely excised.
Given the prior incomplete excision of the lesion and its periocular location, we treated the patient with MMS. After 6 surgical stages, we continued to see evidence of the neoplasm as it tracked medially along the orbicularis oculi muscle (Figure 2). Due to the patient’s physical and emotional exhaustion at this point, we discontinued MMS and referred her to a colleague in plastic surgery for further excision of the remaining focus of positivity as well as repair. The final Mohs defect measured 4.2×4.0 cm (Figure 3). Approximately 2.3×1.0 cm of tissue in the area of remaining tumor was excised by plastic surgery, and the defect was repaired with a cervicofacial advancement flap closure of the right cheek and lower eyelid and full-thickness skin graft of the left upper eyelid. Histopathologic investigation found the additional tissue resected to be free of residual tumor.
Figure 2. Primary mucinous carcinoma tracking medially along the orbicularis oculi muscle (H&E, original magnification ×40).
Figure 3. The final Mohs defect from the primary mucinous carcinoma measured 4.2 × 4.0 cm.
To diagnose a patient with PMC, one must first rule out cutaneous metastasis of various internal malignancies that may appear similar on histopathology. A full clinical investigation consisting of a thorough history, physical examination, and appropriate radiographic imaging is required. Cutaneous metastases most commonly arise from the breast or gastrointestinal tract (GIT) but also can originate from the prostate, lungs, ovaries, pancreas, and kidneys.5 Histologically, PMC may be identical to metastatic adenocarcinoma.13 Location on the body may be a clue to a lesion’s origin, as metastases from a mucinous adenocarcinoma of the breast typically occur on the chest, breast, or axilla,5 whereas PMC primarily is found on the head and neck.