Yes -- about five times as likely as the general population. The connection has long been suspected but only recently has been confirmed.
A six-year study based in Ontario, Canada, was published in the mid-2000s, with a follow-up published in the fall of 2012. The first was designed to explore a connection between elevated incidences of breast cancer among women who had worked in the agriculture industry, but also determined the connection was even stronger among women who had worked in both agriculture and automotive manufacturing. In other words, working on a farm increases risk; going to an auto plant at some point after the farm work increases risk even more. The study also suggests that early exposure to these conditions (during adolescence or puberty) can predispose a woman to developing breast cancer later in life. The study authors were initially approached by a group of Windsor plant employees in the 1970s, and have completed a number of studies on occupational hazards, each providing more detailed findings than the previous one. A 1994 study showed that female auto workers were not at higher risk for breast cancer, but more recent studies contradict that finding [source: Brophy].
The study compared 299 breast cancer patients to 237 patients with other forms of cancer. In addition to the womens' occupations, it took into consideration other relevant factors such as pregnancy history, hormone therapy, past tobacco use, family medical history and residing in proximity to a farm. Since those factors are all known or believed to affect cancer risk, the study's authors cannot attribute cancer cases directly or solely to the workplace -- they can only note whether the population studied was at higher risk.
The 2012 follow-up study zoomed in on the automotive industry, and determined that female auto plastics workers are five times more likely to develop breast cancer than the general population. They are also more likely to be diagnosed with the disease earlier in life; the average breast cancer patient is in her 60s, but factory and farm workers tend to get breast cancer two or three decades earlier.
There are more than 200 known chemical substances that may trigger the development of breast cancer [source: Brophy]. This list includes pesticides, solvents, hydrocarbons (the same poisonous, polluting toxins that contribute to global warming) and plastics. An auto factory worker might not be too concerned about exposure to pesticides, unlike her agricultural industry counterparts, but the rest of these chemicals are a huge source of concern. Chemicals that are commonly found in occupational (work-related) environments have been shown to cause breast cancer in tests conducted on animals; organic solvents in particular have been shown to cause mammary tumors, and can show up in the breast milk of a subject with steady exposure to the toxin.
For a long time, female factory workers knew their environment was unpleasant and probably sickening, but they didn't know the odors, dust, and toxic fumes could actually be fatal. Women who have spent their adult lives working at plastics plants know not only of the effects on their own health, but that of their coworkers -- some have told reporters that friends on the production lines have suffered high instances of nausea, bladder cancer, infertility and miscarriages. Data for these problems and other related health issues haven't been studied -- though the link between certain conditions and certain toxins is established, it hasn't been tied to the factories -- but such anecdotes illustrate that the female factory workers suspected or knew their work environments were unhealthy and dangerous [source: Morris].