Occult cause of paraneoplastic acanthosis nigricans in a patient with known breast dcis: case and review.

Paraneoplastic acanthosis nigricans (pan) is an infrequently encountered cutaneous manifestation of internal malignancy. Here, we describe a case of pan in the setting of a known breast ductal carcinoma in situ, which, to our knowledge, had not been described in association with pan. As a result, thorough investigation was undertaken to search for another concurrent neoplasm that would better explain the development of pan. In so doing, we identified a coexisting metastatic cholangiocarcinoma. We thus conclude that when pan is observed in an uncommon association with a known malignancy, further investigation should be undertaken to explore whether a more likely occult culprit exists.