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Indian Journal of Cancer, Vol. 48, No. 3, July-September, 2011, pp. 296-297 Editorial Breast cancer and lifestyle R Bharath, P Narayanan Department of Medical Oncology, Majumdar Shaw Cancer Institute, Bangalore, India Code Number: cn11080 PMID: 21921326 DOI: 10.4103/0019-509X.84919 Any attempt at understanding the causal link between cancer and lifestyle factors is fraught with many pitfalls. This becomes more confusing in retrospective studies when the factors have taken place a time point remote from the time of interview. The retrospective paired case control analysis published in this edition by Lodha et al. in identifying breast cancer risk factors needs to be appreciated, especially because of the great challenges faced in India in effective and regular follow-up after cancer diagnosis/therapy. The hormone-sensitive nature of breast cancer has triggered the logical exploration of endocrine influences, in general, and estrogen exposure, in particular, in the development of breast cancer, including age of menarche/menopause, parity, duration of breast feeding, exogenous hormone therapy/estrogen treatment, etc. The use of exogenous estrogens in OCP has shown inconsistent association with risk of breast cancer development. The challenges in risk factor assessment done at a time point remote from the development of cancer are reflected in the author's discussion where the history of OCP use is unreliable. Shapiro et al[1] conducted one of the earliest large prospective epidemiological studies on breast cancer risk factors, enrolling more than 60,000 women on follow-up, which did not report an association between breast cancer risk and duration of breast feeding. The authors note that there existed a trend away from breast feeding in the US during the study period, which might have influenced the result. However, the same study also indicates the lower incidence of breast cancer with higher parity (≥3). At around the same time, Yuasa and MacMohan [2] published their case control study of Japanese women where the incidence of breast cancer was low. This study too did not reveal any protective effect of even prolonged lactation among Japanese women. However, other studies showed a trend toward decreased risk of breast cancer with increasing duration of breast feeding, especially in countries with high prevalence. [3],[4],[5],[6],[7] These studies were conducted prior to the era of widespread use of exogenous hormones, hormone replacement therapy (HRT) oral contraceptive pills (OCP). Many of the subsequent investigators have since assessed the risk of exogenous hormone treatments including OCPs. One of the largest collaborative re-analysis consisting of data from more than 150,000 women interestingly demonstrated only an increase in risk of breast cancer during the actual use of OCP, with a relative risk of 1.24. [8] This increased risk declined after discontinuation of OCP and was not evident at 10 years. [7],[8] Many smaller studies including the Nurses Health study, US. [9] did not find increased risk of breast cancer in former OCP users. Various smaller studies have shown inconsistent results. The authors of the current study published in this edition have rightly pointed out the inconsistencies in recollection of OCP use duration among the participants. A bias with more women with breast cancer giving history of OCP use/recollecting longer usage is possible, but difficult to eliminate in a retrospective study. Furthermore, the bivariate analysis used by authors may not have the statistical strength to make the associations valid in this relatively small study. Many small studies have also demonstrated a lower risk of breast cancer with higher degree of parity, which is surprising in developing nations where higher parity is generally associated with longer cumulative duration of breast feeding. These inconsistencies and recall bias will remain a confounding factor in all retrospective studies. Among more recent studies evaluating the epidemiological risk factors, the California Teachers Cohort is noteworthy. [10] This analysis which included 52,464 women did not report decreased risk of breast cancer with higher duration of breast feeding. However, the authors have reported a decrease in breast cancer incidence in women with higher order of parity and a significant decrease in breast cancer in women who have experienced pregnancy at an earlier age. [10] Hadjisavvas et al reported results from a case control study of more than 2000 Cypriot women which showed a protective effect of breast feeding in the development of breast cancer. [11] They noted that a family history was one of the strongest risk factors associated with the development of breast cancer. The Barbados National Cancer Study which included 281 breast cancer patients and 481 matched controls also reported higher incidence of breast cancer in women with family history and the protective effect of earlier pregnancy and higher number of full-term pregnancies. [12] The results reported by Tehranian et al in Iranian women are consistent with the results from the current study. [13] There is, however, a surprisingly discordant report from Pakistan by Fatima et al of the increased risk of breast cancer with multiparity and longer duration of breast feeding. [14] Anovulation during pregnancy and consequent decrease in endogenous estrogen exposure has long been thought to be protective for the development of invasive breast cancer. This has been demonstrated in many studies. However, the effect of prolonged breast feeding has been inconsistent and large cohort studies do not report a protective effect. Lower age at first pregnancy has consistently shown a decrease in the incidence of breast cancer in postmenopausal women. Although the use of exogenous estrogens and OCP has been hypothesized to increase the incidence of breast cancer, these fears have not been conclusively proven in large studies. The incidence of breast cancer does seem to be mildly increased during the use of OCP, but this effect is not evident on long-term follow-up of women who have discontinued OCP. Issues like timing of pregnancies, number of pregnancies and, to a lesser extent, use of OCP depend on various social, cultural, economic, religious, personal choices and other factors and may provide us with an insight into the endocrine milieu which may increase the predilection to develop breast cancer. While strategies to offset these endocrine influences may be attempted, an actual modification of these behavior and lifestyle issues in the community may not be always feasible. The use of exogenous estrogens and hormones on the other hand needs to be evaluated in a well-conducted prospective fashion and safe alternatives need to be identified. The need of the hour is to study large cohorts and follow them over time to identify the risk factors in a prospective fashion. The development of hormone therapy with selective estrogen receptor modulators, antiestrogens and aromatase inhibitors [15],[16] in a community to prevent the development of invasive breast cancers mandates the need for identifying the endocrine risk factors accurately. References
Copyright 2011 - Indian Journal of Cancer |
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