Delayed childbirth may increase lobular breast cancer risk
MedWire News: Women who give birth for the first time aged over 30 years are at increased risk for lobular breast cancer compared with their counterparts who are under 20 years of age, research shows.
Results of the case-control study of approximately 50,000 women also raise awareness that the incidence of lobular breast cancer is likely to increase due to societal changes in childbirth practices and lifestyle factors that contribute to obesity.
Breast cancer incidence and mortality increased in the USA from the 1940s to 1970s. This rise could have been due to a trend toward older age at first birth (AFB) and nulliparity, suggest lead author Polly Newcomb, from the Fred Hutchinson Cancer Research Center in Seattle, Washington, USA, and colleagues.
Previous evidence also indicates that later AFB may be associated more strongly with lobular than ductal breast cancer.
To investigate further, the team recruited a total of 23,382 women with a primary invasive breast cancer from registries in Wisconsin, Massachusetts, and New Hampshire, along with 26,677 controls who were selected randomly from lists of licensed drivers and Medicare beneficiary files.
The participants were interviewed to assess their complete reproductive history, menstrual experiences, medical history, medication use, and lifestyle factors including smoking, alcohol intake, physical activity, and adult height and weight.
The results showed that participants with a higher AFB were more likely to develop breast cancers of all histologic types, including ductal, lobular, and mixed ductal-lobular carcinoma, and that this increase was greatest for lobular carcinoma.
Compared with patients with an AFB <20 years, those with an AFB >30 years had odds ratios (ORs) of 2.38 for lobular breast cancer, 1.31 for ductal breast cancer, and 1.55 for mixed ductal-lobular breast cancer.
Nulliparous women also had higher odds for breast cancer than women who had a child before the age of 20 years, and this association was stronger for lobular than ductal carcinomas (ORs=1.72 vs 1.19).
Further findings reinforced suspected associations between breast cancer and lifestyle factors, including weight and use of hormone-based treatments including contraceptives and hormone replacement therapy.
A later AFB was also a more prominent risk factor for all breast cancer subtypes in women who had never used oral contraception compared with those who had ever used it.
In addition, the risk for lobular breast cancer increased progressively for women in higher categories of body mass index.
The researchers conclude in the journal Cancer: "Temporal changes in childbearing practices and lifestyle factors that influence obesity may lead to an increasing prominence of lobular breast cancer in the coming years."
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By Cher Thornhill