Dark purple skin or mouth nodules are characteristic of which condition?

Dark purple skin or mouth nodules are indeed characteristic of Kaposi's sarcoma. This type of cancer is associated with infection by human herpesvirus 8 (HHV-8), also known as Kaposi sarcoma-associated herpesvirus. The appearance of these nodules is due to the proliferation of blood vessels (angiogenesis) that occurs in this condition. Kaposi's sarcoma often presents as raised, purple lesions on the skin, but can also manifest in the oral cavity, particularly in immunocompromised individuals such as those with HIV/AIDS.

In contrast, melanoma typically presents as darkly pigmented moles or lesions, but it is not characterized by the dark purple nodules seen in Kaposi's sarcoma. Squamous cell carcinoma and basal cell carcinoma are skin cancers that present differently, often with scaling, crusting, or ulceration rather than the distinctive vascular lesions associated with Kaposi's sarcoma. These other carcinoma types do not typically exhibit the dark purple nodules that are specifically linked to the vascular nature of Kaposi's sarcoma.