Estrogen receptor content and ploidy of human mammary carcinoma

In 46 cases of invasive ductal mammary carcinoma the relationship between estrogen receptor (ER) content and ploidy was investigated. Seventy-one percent of the diploid tumors were ER+ against 40% ER+ tumors in the nondiploid group. Forty percent of the ER+ cases had nondiploid tumors and in several of these more than one tumor cell population could be demonstrated. The results support the hypothesis that multiclonal or mosaic composition of the tumor may explain why 30-45% of the patients with apparently ER+ tumors do not respond to endocrine therapy.