Limitations of Immunohistochemistry in Diagnosis of a Primary Mucinous Carcinoma of the Skin and Its Metastasis

Abstract

We describe the case of a 67-year-old female patient who presented with an unclear swelling on the right supraclavicular neck, two years after resection of a mucinous carcinoma on the right mastoid. Two pathological reports from separate universities diagnosed the primary mastoid skin lesion as a metastatic adenocarcinoma. Strikingly, GATA binding protein 3 (GATA3) and mammaglobin, both immunomarkers found in breast cancer, were positive. An urgent search for the primary tumor most likely in the breast was commenced. However, as no other primary tumor could be detected at that time, a Primary Mucinous Carcinoma of the Skin (PMCS) was also debated. Two years later neck node enlargement was suspicious for lymph node metastasis during ultrasound examination and conservative neck dissection was performed. Immunohistochemistry revealed again GATA 3, Mammaglobin, estrogen, and progesterone receptor positive tissue. Using a variety of other markers, we were unable to detect neither significant morphological nor immunohistochemical characteristics that distinguished the lesion from a mucinous carcinoma of mammary origin. Following a detailed review of the clinical context, we concluded the lesion to be consistent with a late metastasis of a PMCS. This report demonstrates the limitations of currently used histopathological and immunohistochemical differentiation in metastatic mucinous carcinoma.