Squamous cell tumors in SPCA1 heterozygous mice. Carcinomas and papillomas were observed in keratinized epithelia of SPCA1 heterozygous mice (11), but the incidence was lower and the age of onset later than in SERCA2 heterozygous mice (8,9). A, Moderate hyperplasia of the forestomach in a 23-month-old heterozygous male; this phenotype was rarely observed in SPCA1 heterozygous mice, but was invariably observed in forestomach of SERCA2 heterozygous mice by 3 months of age. B, Poorly differentiated skin carcinoma in 22-month-old heterozygous male. C, Papilloma with severe hyperkeratosis from peri-anal region of 22-month-old heterozygous male. Bar = 100 micrometers in A and B, 200 micrometers in C.