Evidence from epidemiological studies suggest that different histological types of ovarian cancer have different risk factors. This is consistent with the hypotheses that different ovarian cancer subtypes have different origins.Nulliparity is associated with a greater risk of endometrioid and clear cell ovarian tumors, which may indicate that infertility is associated with these subtypes, a recent study suggests.Epidemiological studies have demonstrated a decreased risk of ovarian cancer among women who have had children and an association between infertility and increased risk of ovarian cancer; however, not many studies have assessed the effects of infertility in nulliparous women.“Ovarian cancer is the seventh leading cause of cancer death among women worldwide, and the fourth leading cause among women in the UK,” explained Kezia Gaitskell, MD, of the University of Oxford, Oxford, UK. “The majority of women with ovarian cancer are diagnosed with advanced disease (stage III to IV). For women who are diagnosed with ovarian cancer, the average 5-year survival is about 30-40%, and this has not improved substantially for many years,” she continued.“We therefore think it is really important to try to understand the origins of ovarian cancer better, as this may ultimately help with more effective prevention, detection, and treatment,” Gaitskell said.This study was published in the International Journal of Cancer and was designed to evaluate the association between reproductive factors and risk by ovarian cancer subtype.
“Our research looks at the risk factors associated with developing ovarian cancer,” Gaitskell said. “We are particularly interested in the way that the associations with certain risk factors vary between different histological subtypes of ovarian cancer. There is evidence from other research that these different subtypes may have very different origins. For example, many cases of high-grade serous ovarian cancer (the most common subtype) may arise from precursor lesions in the fallopian tubes, whereas some endometrioid and clear cell cancers (less common subtypes) may arise from endometriosis,” she continued.
“If these hypotheses of different origins are true, then we might expect the subtypes to have different risk factors –and this is what we have found in this paper and in other work we have published previously,” Gaitskell explained.
“In this paper, we looked at the association between parity (whether a woman has had children, and how many) and breastfeeding, and a woman's subsequent risk of developing different subtypes of ovarian cancer, in a cohort of 1.1 million UK women, with almost 9000 cases of ovarian cancer,” Gaitskell said.“The study, I think, is an interesting study and a good one,” said Stephen C. Rubin, MD, Chief of the Division of Gynecologic Oncology, Fox Chase Cancer Center, Philadelphia, PA. “It's a large study of the kind that can really only be done in a country that has a national health service and national databases so they can capture more than one million women. I think it provides some interesting results and some food for discussion,” he continued.
At recruitment, women completed questionnaires detailing sociodemographic, reproductive, and health factors. Women were excluded if they had a diagnosis of any invasive cancer other than non-melanoma skin cancer, a previous bilateral oophorectomy, or if parity information was missing. Approximately 1% of women were lost to follow-up before December 31, 2014, and were censored at the date when they were lost.
Parity was defined as the number of full-term pregnancies, including stillbirths, but excluding miscarriages. Total breastfeeding duration was calculated as the sum of breastfeeding duration for each child, with the average calculated as the sum divided by the number of children breastfed.