Malignant Acanthosis Nigricans as a Sign of Gastrointestinal Cancer

The speaker presents a case of malignant acanthosis nigricans in a 59-year-old man with a worsening, itchy rash affecting multiple body areas, including the mouth and groin, along with systemic symptoms such as diarrhea, joint pain, abdominal pain, and feeling unwell. The key teaching point is that malignant acanthosis nigricans is most commonly associated with gastrointestinal malignancy, often appearing around the time the cancer is diagnosed, though it can also occur before or after. In this patient, the rash was linked to known metastatic gastroesophageal junction cancer, not to the newly started immunotherapy nivolumab, so treatment should not be stopped for that reason. The talk reviews that acanthosis nigricans is usually a clinical diagnosis characterized by skin thickening rather than true pigmentation, contrasts malignant causes with the far more common insulin-resistance form, and explains that management focuses on treating the underlying condition. The speaker also mentions emerging reports suggesting EGFR inhibitors may improve some malignant cases and highlights the importance of recognizing the condition as a potential sign of internal cancer.