Purpose Endometrial cancers have long been divided into estrogen-dependent type I and the less common clinically aggressive estrogen-independent type II. Little is known about risk factors for type II tumors because most studies lack sufficient cases to study these much less common tumors separately. We examined whether so-called classical endometrial cancer risk factors also influence the risk of type II tumors. Patients and Methods Individual-level data from 10 cohort and 14 case-control studies from the Epidemiology of Endometrial Cancer Consortium were pooled. A total of 14,069 endometrial cancer cases and 35,312 controls were included. We classified endometrioid (n = 7,246), adenocarcinoma not otherwise specified (n = 4,830), and adenocarcinoma with squamous differentiation (n = 777) as type I tumors and serous (n = 508) and mixed cell (n = 346) as type II tumors. Results Parity, oral contraceptive use, cigarette smoking, age at menarche, and diabetes were associated with type I and type II tumors to similar extents. Body mass index, however, had a greater effect on type I tumors than on type II tumors: odds ratio (OR) per 2 kg/m2 increase was 1.20 (95% CI, 1.19 to 1.21) for type I and 1.12 (95% CI, 1.09 to 1.14) for type II tumors (Pheterogeneity > .0001). Risk factor patterns for high-grade endometrioid tumors and type II tumors were similar. Conclusion The results of this pooled analysis suggest that the two endometrial cancer types share many common etiologic factors. The etiology of type II tumors may, therefore, not be completely estrogen independent, as previously believed.
Bibliographical noteFunding Information:
Supported by a grant from the National Institutes of Health (NIH) National Cancer Institute (NCI; Grant No. CA135632 to V.W.S). V.W.S. is supported in part by NCI K07 Career Development Award (Grant No. CA116543). The individual studies were funded by the following grants: ANECS (National Health and Medical Research Council [NHMRC, Grant No. 339435] of Australia and the Cancer Councils of Queensland and Tasmania; P.M.W. and A.B.S. are supported by Fellowships from the NHMRC); BAWHS (NIH Grant No. R01 CA74877; controls were collected under: NIH Grants No. R01 63446, DAMD 17-96-607, and California Breast Cancer Research Program 4JB-1106); BCDDP (Intramural Research Programs of the NCI, NIH, Department of Health and Human Services, United States); CECS (NIH Grant No. R01 CA098346); CPS-II (the American Cancer Society); CTS (NIH Grant No. R01CA77398 and the California Breast Cancer Research Fund; the collection of cancer incidence data was supported by the California Department of Public Health as part of the statewide cancer reporting program mandated by California Health and Safety Code Section 103885; the NCI’s Surveillance, Epidemiology and End Results Program awarded to the Cancer Prevention Institute of California, University of Southern California, the Public Health Institute; and the Centers for Disease Control and Prevention’s National Program of Cancer Registries); EDGE (NIH Grant No. R01 CA83918); FHCRC (NIH Grants No. R35 CA39779, R01 CA75977, N01 HD23166, K05 CA92002, R01 CA105212, R01 CA87538); HAW (NIH Grants No. P01 CA33619, R01 CA58598, N01 CN67001, N01 PC35137); IWHS (NIH Grant No. R01 CA39742); MEC (NIH Grant No. CA54281); NLCS (the Dutch Cancer Society); NHS (NIH Grants No. P01 CA87262 and R01 CA082838); PECS (Intramural Research Funds of the NCI, NIH, Department of Health and Human Services, United States); SECS (NIH Grant No. R01 CA092585); SMC (the Swedish Cancer Registry, the Swedish Research Council, and the Karolinska Institutet’s Research Funds); US (Intramural Research Funds of the NCI, NIH, Department of Health and Human Services, USA); USC LA (NIH Grants No. R01 CA48774 and P30 CA14089); and WISE (NIH Grant No. P01 CA77596).