A cohort study of 49 933 women with surgically verified endometriosis: Increased incidence of breast cancer below the age of 40

Abstract

Introduction: The association between endometriosis and breast cancer is unclear. We assessed the risk of breast cancer in women with surgically verified endometriosis, with special focus on the age at cancer diagnosis, time from endometriosis diagnosis and breast cancer histology. Material and Methods: All women with first endometriosis associated diagnoses occurring concomitantly with relevant surgical codes during 1987-2012 were retrieved from the Finnish Hospital Discharge Register in Finland. Breast cancers diagnosed after the endometriosis diagnosis were identified from the Finnish Cancer Registry. The Finnish female population served as the reference. The endometriosis cohort consisted of 49 933 women (23 210 cases of ovarian, 20 187 peritoneal and 2372 deep infiltrating endometriosis). The outcome measure was the standardized incidence ratio (SIR) with 95% confidence interval (95%CI) of breast cancer calculated for the whole cohort and for the subtypes of endometriosis, stratified by the age at breast cancer diagnosis, histology, and time from endometriosis diagnosis. Results: The overall risk of breast cancer (1555 cases) was similar to the reference population (SIR 0.99; 95%CI 0.94 to 1.03), did not differ in types of endometriosis, and was similar for ductal and lobular breast cancer. However, the SIR of breast cancer was increased in the age group of 20-29 years (4.44; 95%CI 2.22 to 7.94), and in the age group of 30-39 years (1.28; 1.03 to 1.57). The risk of in situ breast cancer (170 cases) was increased in the entire endometriosis cohort (1.25; 1.07-1.44). Conclusions: The overall risk of breast cancer in women with surgically verified endometriosis was similar to that of general population. However, the risk of breast cancer at young age was increased. Young women with surgically verified endometriosis represent highly symptomatic patients with more frequent surgeries and additional therapies that might also contribute to the risk of breast cancer.

Genetic Contribution of Endometriosis to the Risk of Developing Hormone-Related Cancers

“…Data on the association between endometriosis and breast cancer are less consistent due to different reasons that have been reviewed elsewhere [ 9 , 10 ]. On the one hand, some studies provide evidence that women with endometriosis are more vulnerable to develop breast cancer, although they show contradicting results with regard to the age when this increased susceptibility is observed [ 11 , 12 ]. On the other hand, another group of studies are supportive of a negative association between endometriosis and breast cancer, the former possibly conferring protection from the latter [ 13 , 14 ].…”

Association between breast diseases and symptomatic uterine fibroids by using South Korean National Health Insurance database

“…Although the majority of the studies supported an association between the two, issues regarding the association between endometriosis and BC risk are still inconclusive 46 , 47 . A study reported that the overall risk of BC in women with surgically verified endometriosis was similar to that in the general population 48 . We do not know the exact mechanisms involved in an inverse association between endometriosis and BC, but Matta et al suggested that higher DNA repair capacity (DRC) in women with endometriosis and/or hormonal treatments for endometriosis may provide specific protective effects for BC 49 .…”

Causal effects of genetically predicted endometriosis on breast cancer: a two-sample Mendelian randomization study

“…The standardized incidence of in situ breast cancer increased in the 40-to 59-year-old age group; however, patients with EMS aged 40 years or older might undergo breast imaging more frequently than the general population, which could potentially increase the detection and prompt treatment of in situ cancer and thus reduce breast cancer risk 30 .…”