Differentiation between a primary adnexal carcinoma and a metastatic carcinoma to the skin is a challenging yet critical task for dermatologists and pathologists. Carcinomas that have metastasized to the skin are a sign of widespread systemic involvement and poor prognosis, while primary adnexal carcinomas tend to progress with an indolent clinical course. Although many patients with cutaneous metastases from an internal primary neoplasm can expect a median survival of no more than 12 months,1 patients with primary adnexal carcinomas are reported to have a 5-year survival rate of 95.5% for localized disease and 85% with spread to regional lymph nodes.2 We report a case of multiple cutaneous neoplasms of unknown primary origin in a 71-year-old man and describe our approach to identification of the possible primary site as well as management of the disease.
Case Report
A 71-year-old man initially presented to his primary physician for evaluation of a mass on the left side of the neck of 3 months' duration. On physical examination, a firm 2.5×3.0-cm nodule was noted at the anterior border of the trapezius muscle. Palpation of the thyroid revealed an additional right-sided nodule. The submandibular and parotid glands were unremarkable to palpation. The patient was referred to general surgery for biopsy, which revealed an infiltrating, moderately differentiated adenocarcinoma with extensive lymphatic permeation. Immunohistochemical staining for cytokeratin (CK) 7 was positive, while CK20 and thyroid transcription factor 1 were negative. A positron emission tomography/computed tomography (CT) fusion scan demonstrated 3 areas of enhanced uptake: one in the right side of the thyroid, a second corresponding to the mass on the left side of the neck at the level of the trapezius muscle, and a third in the left masseter muscle. Surgical excision with negative margins with possible chemotherapy was recommended; however, the patient declined treatment and was lost to follow-up until 2 years later when he presented to his primary physician with an additional lesion on his scalp.
Four years after the biopsy, the patient presented to the dermatology department with additional tumor nodules including a 4-cm, annular, indurated, focally eroded plaque on the left side of the lateral neck (Figure 1); 3 separate 1-cm nodules on the right side of the lateral neck; and an ulcerated, crusted, 10×8-cm plaque on the posterior aspect of the scalp. Despite the extensive lesions, the patient remained in good health and reported no recent weight loss or signs or symptoms of systemic involvement. The posterior scalp lesion, which developed 2 years after the initial appearance of the mass on the neck and was thought to represent a possible metastasis of the tumor, was biopsied and showed diffuse infiltration of the dermis by poorly differentiated tumor cells with vacuolated cytoplasm arranged in nests and cords and sometimes in a single-file arrangement (Figure 2). A CT scan demonstrated pretracheal lymphadenopathy as well as small intraparenchymal and subpleural pulmonary nodules throughout both lung fields.
Figure 1. Indurated ulcerated plaque on the left side of the lateral neck 5 years after initial presentation.
Figure 2. Histopathology of a posterior scalp lesion demonstrated irregular nests and confluent islands of undifferentiated tumor cells infiltrating the upper dermis, approaching but not connected to the epidermis, along with rounded to ovoid nuclei and abundant eosinophilic cytoplasm (H&E, original magnification ×100).
Another scalp biopsy was taken. Tumor cells were negative on mucicarmine staining. Additional immunohistochemical staining, including a periodic acid-Schiff stain with diastase digestion for epithelial mucin revealed minimal luminal positivity. Immunostaining was positive for CK7, carcinoembryonic antigen, CD15, estrogen receptor, progesterone receptor, gross cystic disease fluid protein 15 (GCDFP-15), and mammaglobin, and negative for CK20, podoplanin, thyroid transcription factor 1, S-100 protein, p63, and prostate specific antigen. ERBB2 (formerly HER2/neu) staining was negative according to fluorescence in situ hybridization analysis. Tumor cells showed a Ki-67 nuclear proliferation index of greater than 50%, indicating progression to aggressive carcinoma.
Based on the histological and immunochemical studies, the differential diagnosis included primary cutaneous apocrine carcinoma versus breast carcinoma; however, the prolonged clinical progression of these lesions favored a primary cutaneous adnexal tumor over a metastatic adenocarcinoma. Nevertheless, despite the initially indolent growth of the lesions over the first 5 years, the Ki-67 proliferation index and presence of widespread metastases on the posterior scalp indicated progression to an aggressive carcinoma. Chemotherapy was recommended as the treatment of choice. At his most recent follow-up visit 4 months later, the patient chose to begin treatment with tamoxifen and refused other treatment options.