static breast carcinomas demonstrate CK20-negativity (CK20−) and CK7-positivity (CK7+) by immunohistochemistry. Herein, we report a case of metastatic breast carcinoma to the skin with variant CK20+/CK7− immunophenotype. A 72-year-old...
morestatic breast carcinomas demonstrate CK20-negativity (CK20−) and CK7-positivity (CK7+) by immunohistochemistry. Herein, we report a case of metastatic breast carcinoma to the skin with variant CK20+/CK7− immunophenotype. A 72-year-old white female presented to the dermatology clinic with a mass on her right chest, of recent onset. She had been diagnosed with primary breast cancer (ductal carcinoma) 41 years prior, with a subsequent history of widely metastatic disease to noncutaneous sites over recent years. Review of histopathology reports revealed that previously biopsied systemic tumor expressed a CK20+/CK7− immunophenotype. A skin biopsy was performed. Histopathological analysis showed an infiltrating intradermal adenocarcinoma composed of pleomorphic, hyperchromatic tumor cells with evidence of ductal differentiation (Figure 1A,B). By immunohistochemistry, tumor cells were reactive for Cam 5.2, ER, GATA3, and CK20; and negative for CK7, PR, CDX2, and villin (Figure 1C,D). The histopathologic features and immunohistochemical results supported the diagnosis of cutaneous metastasis of the patient's known breast carcinoma with variant CK20+/CK7− immunophenotype. Review of the scientific literature reveals that up to 6% to 8% of breast cancers express CK20+, with 1% to 1.6% of cases showing a CK20+/CK7− immunoprofile, as in our case. The frequency of CK20 positivity is similar in different subtypes of breast carcinoma, but appears to carry prognostic significance. CK20 expression has been reported to be associated with increased stage, metastases, and lower overall survival in breast cancer. In addition, CK20-positive tumors are strongly associated with apocrine features and Her-2 subtype, and with ER and PR negativity. Only one prior example of CK20+/CK7− metastatic breast carcinoma has been reported in the literature. This was a case of a 52-year-old woman with a previous history of breast cancer who presented with a growing cutaneous/ soft tissue mass below the right eyebrow. The main goal of diagnosing skin metastases for dermatopathologists is to determine the histopathological type and primary site. A panel of immunostains is commonly employed, with a simple algorithm combining CK7 and CK20 used to direct further histopathological investigation. The immunophenotype of this patient's skin tumor, CK20+/CK7−, is more typical of metastatic carcinoma of colorectal origin. It is also important to consider that phenotypic instability for CK20, although rare, has been reported during evolution and metastatic spread of breast cancer. These facts highlight the need to obtain a more complete immunohistochemical profile that includes differentiation-specific markers, in addition to the importance of correlation with clinical history and immunophenotypic profile of previously sampled tumor when making the correct diagnosis, as in this case.