Commentary

Cigarette smoking and risk of breast cancer in women

Multiple studies provide estimates of the risk of breast cancer for women. Dense breasts on mammography or having first-degree relatives with breast cancer are associated with at least a 2-fold increase in risk of breast cancer. Prior breast biopsy, second-degree relatives with breast cancer, or heterogeneously dense breasts are associated with a 1.5- to 2.0-fold increased risk; current use of oral contraceptives, nulliparity, and age 30 years or older at first birth are associated with a 1.0- to 1.5-fold increased risk. Predisposing genetic mutations, lobular carcinoma in situ, and atypical hyperplasia increase risk markedly. These risk factors, as well as environmental exposures, are reviewed in this chapter. Identification of these risk factors may be useful for personalized management of breast cancer risk.

Several approaches have been suggested for incorporating risk factors to predict the future risk of breast cancer. The Breast and Ovarian Analysis of Disease Incidence and Carrier Estimation Algorithm (BOADICEA) and International Breast Cancer Intervention Study (IBIS) are among these approaches. We compared the performance of these models in discriminating between cases and noncases in the Iranian population.

We performed a case-control study in Tehran, from November 2015 to April 2016, and enrolled 1633 women aged 24 to 75 years, including 506 cases of breast cancer, 916 population-based controls, and 211 clinic-based controls. We calculated and compared the risk of breast cancer predicted by the IBIS and BOADICEA models and the logistic regression model. For model discrimination, we computed the area under the receiver operating characteristic (ROC) curve.

The risk of breast cancer predicted by the IBIS model was higher than the BOADICEA model, but lower than the logistic model. The area under the ROC plots indicated that the logistic regression model showed better discrimination between cases and noncases (71.53%) compared with the IBIS model (49.36%) and BOADICEA model (35.84%). Based on the Pierson correlation coefficient, the correlation between IBIS and BOADICEA models was much stronger than the correlation between IBIS and logistic models (0.3884 and 0.1639, respectively).

The IBIS model discriminated cases and noncases better than the BOADICEA model in the Iranian population. However, the discrimination of the logistic regression model, which included a larger array of familial, genetic, and personal risk factors, was better than the 2 models.

A 70-year-old female patient with prior breast cancer was diagnosed with colorectal carcinoma six years following the original breast referral. The cancers were both discovered at an early stage enabling potentially curative surgery to be performed, with an associated good long-term prognosis. This article explores a range of cancer risk factors associated with lifestyle, genetics and medication to ascertain whether the two primary cancers were independent oncological events, or whether they were related. Factors such as smoking, alcohol consumption, genetic predisposition and the use of contraceptives and Tamoxifen may increase the relative risk for both cancers. Various studies have offered conflicting data regarding the relative risk for developing the second cancer, but long-term cohort studies will continue to add to the evidence base. It is possible that the outcomes of these studies may have implications for the follow up of breast cancer patients within the colorectal cancer screening service.