Skin affected by a burn cancer is scarred, ulcerated, and often appears as erythema ab igne clinically in adjacent skin. The latent period in burn scar malignancy is much longer for SCC than BCC. Malignant melanoma and various sarcomas are reported to arise in burn scars, too. The other extreme on the temperature scale can less often result in enough permanent acral damage that poor wound healing may eventually result in cancer, usually SCC. About 1% of patients with chronic osteomyelitis develop cancer, usually SCC in sinus tracts. As with tumors arising in burn scars and chronic leg ulcers of varied etiology, black patients are disproportionately overrepresented in osteomyelitic malignancy. In nearly all of the patients with radiation-induced skin cancer, concomitant radiodermatitis is present. As with burn scar and osteomyelitic cancer, x-ray related cancer has a long latent period. Similar to burn scar cancer, SCC predominates in osteomyelitis and occurs on the extremities. BCC, when it arises, is more common on the face and neck in burn- and radiation-induced tumors. Multiple tumors are frequent as is recurrence in x-ray malignancy. Mortality is high: one out of three to four patients with burn scar, osteomyelitic, and radiation cancer die of dermatosis-related malignancy. Recently, radioactivity-contaminated gold rings have been implicated in causing SCC. Carcinoma tends to occur in irradiated benign dermatoses whereas sarcomas tend to complicate irradiated malignancies. Stasis ulceration and anogenital fistulae may rarely lead to cancer, SCC in the former and adenocarcinoma in the latter. SCC can rarely develop in four related conditions (acne conglobata, dissecting perifolliculitis of the scalp, hidradenitis suppurativa, and pilonidal sinus) after a lengthy latent period; prognosis is poor with a high metastatic rate. A whole host of chronic cutaneous infections can lead to malignancy occasionally; these include lupus vulgaris, lymphogranuloma veverum, granuloma inguinale, leprosy, actinomycosis, and candidiasis. BCC more than SCC is known to complicate smallpox vaccination sites. Certain erosive and/or scarring dermatoses other than those mentioned above can be unusually affected by secondary malignancy. Discoid lupus erythematosus lesions often subjected to the carcinogenic effects of sunlight can degenerate into SCC in patients with either light or dark skin. In acrodermatis chronica atrophicans, a condition not often seen in the United States, the involved skin, particularly of the lower extremities, is susceptible to SCC, lymphoma, and BCC. Epidermolysis bullosa, especially the recessive dystrophic variant, can be complicated by SCC on affected mucous membrane and acral skin.(ABSTRACT TRUNCATED AT 400 WORDS)