Sex differences in cancer mortality among solid organ transplant recipients

Males have increased mortality after a cancer diagnosis than females, possibly due to poorer immunosurveillance. We tested whether the female survival advantage is lost with immunosuppression by evaluating 17,048 cancer patients (68% male) with a prior solid organ transplant using data from the US Transplant Cancer Match Study and 1,221,914 cancer patients (58% male) from the general population using data from the Surveillance, Epidemiology, and End Results Program. We evaluated 13 solid cancers that occur in both sexes. We compared mortality due to cancer in males and females using a male:female hazard ratio (M:F HR) derived from Cox proportional hazards models adjusted for age, race/ethnicity, diagnosis year, stage, and cancer treatment. Among cancer patients in the general population, males had higher cancer-specific mortality than females for cancers of the lip, stomach, colorectum, anus, liver, lung, skin, brain, and thyroid, with M:F HRs ranging from 1.06 to 1.59. Only colorectal cancer showed an attenuation in the female mortality advantage in transplant recipients (M:F HR_Transplant: 0.89; 95% CI: 0.77, 1.03; vs. M:F HR_GenPop: 1.07; 95% CI: 1.06, 1.08; P-interaction = 0.007). Among kidney cancer patients, the female mortality advantage was stronger in the transplant population (M:F HR_Transplant: 1.33; 95% CI: 1.11, 1.60; M:F HR_GenPop: 1.02; 95% CI: 0.99, 1.04; P-interaction = 0.003). Overall, we did not find consistent evidence that the female advantage in cancer mortality is weakened among immunosuppressed transplant recipients, suggesting that non-immune factors contribute to the female advantage among cancer patients in the general population.