The nuclear DNA content of cells of "apocrine metaplasia" was measured in 9 cases of fibrocystic disease of the breast. Three vulvectomy specimens containing true apocrine glands were used as controls. The microspectrophotometric measurements were carried o u t by the "plug" method on paraffin sections stained by the Feulgen reaction. Initially, the lesions were histologically graded from 1 t o 3 according to the degree of cellular proliferation. The distribution of nuclear DNA in the true apocrine gland cells of the vulva had a restricted diploid distribution. T h e "apocrine" areas all contained a tetraploid population, but the proportion of tetraploid cells significantly increased with increasing histologic grade. In one case, a grade 3 metaplasia, there was a hyperdiploid-aneuploid DNA distribution pattern. T h i s patient developed invasive carcinoma of the breast subsequent to the biopsy procedure.
T HAS BEEN ACCEPTED THAT THE "APOCRINE
I metaplasia" found in fibrocystic disease of the breast is one of the characteristic features of the disease, and that it most commonly occurs in the fourth and fifth decades.8-28 The size of these apocrine-like cells varies from two to four times that of the normal mammary epithelia cell. The nuclei are round, large, and vesicular, and the abundant, pale, sometimes faintly granular, cytoplasm stains pink with eosin and yellow with van Gieson's stain.