A Rather Misleading Study

According to the American Cancer Society, the medications used in IVF assisted reproductive treatment can cause cancer.  In a recent Medscape editorial, however, Dr. Arefa Cassoobhoy argues that a new study of 250,000 British women proves that exposure to the high levels of hormones used by reproductive specialists does not significantly increase cancer risk.  Based on the size of the study and the fact that the women were tracked for an average of 9 years after IVF care, the results of the British study seem compelling.

The epidemiology of reproductive system cancers in women, however, raises some questions.  For breast and ovarian cancers the mean age is in the early 60’s.  Since the average age of the recipients of IVF treatment in the study was 35 and the researchers followed patients for an average of 9 years, the majority of the women were only studied until age 45.  In other words, the U.K. research team stopped looking at the subjects almost two decades before they were statistically likely to be diagnosed with cancer. 

There is an argument to be made that if cancer occurred more than 9 years after treatment it would not be a direct consequence of the IVF treatment.  Although the better part of a decade may seem like more than enough time to figure out whether or not a carcinogen has resulted in cancer, a review of latency periods challenges this assumption.  In fact, for many kinds of cancer, the time between exposure to a carcinogen and the onset of a cancer, the latency period, is measured in decades.  This explains how a patient who quit smoking 15 or 20 years earlier might still end up with lung cancer.

Given the lengthy duration and notable size of the UCL Great Ormond Street Institute of Child Health study, the good news is that cancer risk from IVF fertility medications during the first decade subsequent to treatment has been shown to be reassuringly low.  But, as the study’s researchers themselves observed, "We cannot exclude the possibility of different risk profiles for any studied cancer on longer follow-up, at ages when most reproductive-related cancers occur."  If we want "to put the IVF-Cancer connection to bed", as Dr. Cassoobhoy suggests, further studies of women who have received fertility medicines and whose age puts them at high risk of developing a reproductive system cancer are essential.