A 75-year-old man presented with recurrent pruritic eczema of the penis and scrotum that was refractory to medication of the local dermatologic clinic for one and a half years. The lesion consisted of an erythematous and indurated plaque with ulceration and exudation (). Review of the patient's history revealed that he underwent right hemicolectomy for adenocarcinoma in the ascending colon when he was 62 years old. He remained under regular follow-up for 13 years, during which no metastases were reported. Examination of skin biopsy from the inguinal folds revealed large cells with clear to eosinophilic cytoplasm that had infiltrated into the epidermis, singly and in clusters (). The initial histologic diagnosis of the skin biopsy was EMPD. The preoperative instrumental investigations showed no evidence of recurrence on the previous surgical site or other underlying internal malignancy. The patient underwent a mapping biopsy at multiple sites to accurately establish the boundary of the lesion, followed by wide excision and closure of the defect with a skin graft.\nThe resected perineum and penile shaft showed ill-defined indurated nodules with a firm consistency. The lesion in the overlying epidermis measured 6 cm, with a 1.5-cm-sized mass in the dermis. The cut surface was solid and gray-white with focal mucinous appearance. On histologic examination, the lowpower view showed a relatively well-defined mass occupying the dermis and subcutis (). The overlying epidermis showed irregular epidermal hyperplasia containing scattered large cells arranged singly or in groups, as in the previous skin biopsy, suggesting an epidermal pagetoid spread of underlying tumor cells (). The tumor showed two composite features in which solid nests of poorly differentiated carcinoma were juxtaposed with paucicellular mucinous lakes with floating tumor cell clusters (). The latter accounted for the majority of the tumor, about 70%, and the rest consisted of poorly differentiated components. Tumor cells in both the mucinous pool and more cellular area revealed the same histological features of abundant eosinophilic cytoplasm and large vesicular nuclei with frequent mitoses up to 7/10 high power field (, ). In situ lesions similar to ductal carcinoma in situ of the breast were also observed () with colonization of the hair follicles (). Overall histology suggested a mucinous carcinoma with minor poorly differentiated components.\nHistological differential diagnosis included PCMC and late metastasis of the previously diagnosed colon cancer. Histologic review of the patient’s previous colon cancer showed a 4.3-cm moderately differentiated adenocarcinoma with the assigned stage of T3N0M0. The tumor consisted of well-formed or cribriform patterns of tumor glands with frequently observed dirty necrosis (). There was no mucin production observed in the skin lesion.\nImmunohistochemical studies were performed. The Paget’s and dermal tumor cells of the skin lesion were positive for cytokeratin (CK) 7, CK20, gross cystic disease fluid protein-15 (GCDFP-15) (–), and carcinoembryonic antigen (CEA), but negative for caudal-related homeobox gene 2 (CDX-2). On the other hand, tumor cells of the colon cancer were positive for CK20, CDX-2, CEA, but not gross cystic disease fluid protein 15 or CK7. Additional staining of human epidermal growth factor receptor 2 and estrogen receptor (ER) was observed in the skin lesion (, ), but the lesion was negative for progesterone receptor (PR). Myoepithelial cells surrounding the carcinoma in situ were highlighted by CK5/6 immunostaining (). The overall immunohistochemical findings of the skin lesion were different from those of colon cancer but similar to those of breast cancer, but similar to those of breast cancer, indicating sweat gland origin. On the basis of these histologic and immunohistochemical findings, the two malignancies were considered to differ in origin, and the present case was a primary mucinous carcinoma of the skin.\nAnother challenge was to determine whether the minor poorly differentiated components were eccrine or apocrine in origin because there was no clear distinction in histologic and immunohistochemical features. We concluded apocrine differentiation of the lesion due to the location in the groin, where apocrine glands are many in number, and to the resemblance of apocrine carcinoma in the breast even though decapitation secretion was absent. In addition, close approximation and colonization of the hair follicle () favored the origin of the follicularapocrine unit.\nThe final pathologic diagnosis was PCMC with EMPD showing apocrine differentiation.\nThis case was approved by the institutional review board (IRB) of Kosin University Gospel Hospital, and informed consent was waived by the IRB (IRB reference number: 2017-10-010).
A 39-year-old Japanese male presented with a 3 months history of a skin tumor on the left side of the jaw. Past medical history revealed lung tuberculosis at age 20 years old. Physical examination showed a dome-shaped, slightly erythematous nodule measuring approximately 2 cm in diameter (Fig. ). Preoperative examination revealed no lymph node or distant metastasis. Punch biopsy was performed, and it was diagnosed as mucinous adenocarcinoma of the skin.\nThe tumor was excised with 5-mm surgical margin and was reconstructed with local rotational flap. The definitive histopathology showed small cellular nests of adenocarcinoma lying in pools of extracellular mucin that were separated by fibrocollagenous septae without involvement of underlying muscle. (Figure a,b) The immunohistochemical staining revealed that the tumor cells were positive for CK7, epithelioid membrane antigen (EMA), MUC1, MUC2, estrogen receptor (ER), and progesterone receptor (PR).\nThe patient again noticed a small tumor on the left side of the jaw in the area of the previous operation site 2 years after the primary operation. However, the patient had chosen not to be examined by a physician and left it alone for 4 years. Because of the rapid growth of the tumor, the patient visited our clinic. At this point, the tumor measured approximately 6 cm in diameter (Fig. a). Preoperative examination revealed invasion of the mandible and one left neck lymph node metastasis. The lesion was excised with at least 1-cm border of normal skin including the mandible (Fig. ). A left radical neck dissection was performed, and the mandible was reconstructed with a free scapula flap. The definitive pathology revealed MCS recurrence with no residual tumor cells in the excised normal skin area. One of 20 regional lymph nodes contained metastasis. Postoperatively, the patient was free of tumor and was followed up by the physician in charge every 3 months for 5 years and every 6 months for the next 5 years. The patient was disease-free for ten consecutive years on physical examination, chest X-ray, neck echogram, and ordinary blood test. Although the patient did not have any symptoms, the chest X-ray at the 11th year follow-up revealed multiple lung metastases (Fig. a,b). Additional chest computed tomography (CT), magnetic resonance imaging (MRI), and RI showed cervical vertebrate (Th5) tumor, and biopsy revealed metastasis of MCS. The patient received radiotherapy for pain control and died 3 year after the diagnosis of metastasis.