Red spots could be a sign of cancer, but they are not always. Skin cancer can vary in appearance based on the cancer type. For example: Squamous cell carcinoma can cause a firm red nodule, flat scaly sores, or a red patch inside the mouth or on the genitals or anus. Basal cell carcinoma often causes a white waxy lump or a brown scaly patch on sun-exposed skin. Melanoma is often recognized by changes in an existing mole (including changes in color, size, and borders).