Decreased breast cancer rates among women with choriocarcinoma

We hypothesized that exposure to high levels of hCG in women diagnosed with choriocarcinoma would decrease future breast cancer risk.

We used the Surveillance, Epidemiology, and End Results (SEER) registry limited-use database (1973-2004) to search for placenta tumors (ICD-10 C58), i.e. choriocarcinoma (CC). Demographics were obtained including patient ID, primary site, year of diagnosis, sex, race, DOB, age group and survival months. Patients with initial choriocarcinoma were searched for subsequent breast cancers. The cohort diagnosis with CC and subsequent breast cancers were compared to general population-based rates of breast cancer.

A query for CC yielded 646 women between the ages 15 and 54 years. Of the 646 women, 422 were white, 129 African-American, and 95 "other". Total women-years of observation were 7165.3 with two CC patients developing breast cancer yielding a breast cancer incidence rate of 27.9/100,000 women-years. The incidence rate ratio(IRR) of the CC cohort to the general population was 0.21 (95% CI(0.145-0.327); P<0.01). In women with CC under the age of 35 years the breast cancer rate was 34.1/100,000, IRR 0.27 (95% CI(0.182-0.386); P<0.01). Controlling for race, breast cancer rates in whites were 49.3/100,000 (IRR 0.37, P<0.01); in African-American 1.3/100,000 (IRR 0.01, P<0.001); and 2.6/100,000 (IRR 0.03, P<0.001) in "others" compared to the general population.

Women with prior CC had a 79% reduction in breast cancer risk compared to the general population regardless of age and race. Given the high level of hCG and decreased rate of breast cancer among women with CC, the hypothesis that hCG is protective against breast cancer seems plausible.