Pregnancy-Associated What?!?

During medical training, I learned a lot about post-partum breast cancer. In particular, I learned postpartum breast cancer is generally diagnosed early, is generally treated as an outpatient, and patients generally do well. On my notes from my scientific basis of medicine lecture during second year, I wrote the following regarding pre-menopausal breast cancer: "high grade, generally advanced stage, extremely poor prognosis." The good news is that new treatments, particularly for Her-2 positive disease, have markedly changed the landscape for some pre-menopausal women. When I was in medical school, the major trial on herceptin as an adjunctive chemotherapy agent was ongoing; this drug has proven to be extremely effective for patients with the Her-2/neu receptor. Since then, two more monoclonal antibodies have been developed (kadcyla and pertuzumab) and both show great promise. In addition, data from more recent years shows that, after adjusting for stage of disease at diagnosis, age is not an independent risk factor for poor outcomes, at least for Her2-positive disease.

However, despite all of my medical training, I had never even heard of pregnancy-associated, or post-partum breast cancer.

Conventional wisdom is that pregnancy, particularly prior to age 30, reduces the life-time risk of breast cancer. The dirty little secret: While pregnancies clearly reduce life-time risk, there is actually a slight increase in breast cancer during the intra- and post-partum periods. In fact, approximately 1 out of every 3000 pregnancies will cause breast cancer. Further, there is epidemiologic evidence that pregnancy-associated breast cancer may actually be increasing. This increase has largely been attributed to increasing maternal age, but the underlying cause remains unclear.

One in 3000 is a very small number-- but it is not zero -- and it is a risk that every pregnant and breastfeeding woman should know about. Finding lumps during the intra- and post-partum periods is difficult, because breasts are dense, and clogged ducts are common. However, if a lump is found, it is very, very important to get it checked out-- up to 20% of lumps during pregnancy and lactation turn out to be malignant, and, in general, pregnancy-associated breast cancer is aggressive and nasty-- so early diagnosis is particularly important to ensure the best possible outcome (Note that, after adjusting for stage at diagnosis, the 95% confidence interval crosses one, which means there is no statistically significant difference).