A slowly growing, subcutaneous mass in the left eyebrow region of a 54‐year‐old Japanese woman showed numerous small epithelial cell nests surrounded by a dense desmoplastic stroma. The epithelial cell nests showed partially keratinizing cystic structures containing a small amount of glycogen. Immunoperoxidase staining for carcinoembryonic antigen was positive only in the lumina or on the ductal lining surface of tumor cells; staining for S‐100 protein was positive within almost all of the tumor nests. Birbeck granules indicating Langerhans cells were found within some of the cells.

A 38‐year‐old Japanese male with Bloom's syndrome (BS) and porokeratosis of Mibeili (PM) developed multiple carcinomas of the skin and lung. There were multiple, spontaneous chromosomal aberrations and frequent sister chromatid exchanges (SCE). Cutaneous delayed‐type hypersensitivity reactions were defective and serum IgM was decreased. The lung cancer was treated with radiation, which was effective but caused a severe pulmonary atelectasis and esophageal stricture. The patient expired one‐and‐a‐half years later because of pneumonia. Autopsy disclosed an adenocarcinoma of the colon. The concurrent PM was considered responsible for the occurrence of multiple skin cancers.

Between 1976 and 1988, 135 patients with solar keratosis (SK) and 53 patients with squamous cell carcinoma (SCC) on the sun-exposed skin, but without apparent preceding diseases such as burn scars, chronic radiodermatitis, chronic arsenic poisoning, or xeroderma pigmentosum, were encountered. Sixteen of the SCC patients also had SK on other areas of sun-exposed skin. There were 31 SCC patients also showing SK (SK-SCC) and 22 SCC not showing SK (DN-SCC) within the same histologic sections. The mean ages of the patients with SK-SCC and with DN-SCC were similar. Metastases to regional lymph nodes were observed in 5 SK-SCC patients, of whom 3 died of the disease, and in 5 DN-SCC patients, of whom 4 died of the disease. The five-year post-operative survival rates were 70% in SK-SCC and 74% in DN-SCC; the ten-year post-operative survival rates were 70% in SK-SCC and 44% in DN-SCC.

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