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Background: The relationships between PTEN loss and/or PIK3CA mutation and breast cancer prognosis remain controversial. We aim to examine the associations in large epidemiologic cohorts. Methods: We followed women with invasive breast cancer from the Nurses’ Health Studies with available data on tumor PTEN expression (n = 4,111) and PIK3CA mutation (n = 2,930). PTEN expression was evaluated by IHC and digitally scored (0%–100%). Pyrosequencing of six hotspot mutations of PIK3CA was performed. Results: We found loss of PTEN expression (≤10%) occurred in 17% of cases, and PIK3CA mutations were detected in 11% of cases. After adjusting for clinical and lifestyle factors, PTEN loss was not associated with worse breast cancer-specific mortality among all samples [HR, 0.85; 95% confidence intervals (CI), 0.71–1.03] or among estrogen receptor (ER)-positive tumors (HR, 0.99; 95% CI, 0.79–1.24). However, among ER-negative tumors, PTEN loss was associated with lower breast cancer-specific mortality (HR, 0.68; 95% CI, 0.48–0.95). PIK3CA mutation was not strongly associated with breast cancer-specific mortality (HR, 0.89; 95% CI, 0.67–1.17). Compared with tumors without PTEN loss and without PIK3CA mutation, those with alterations (n = 540) were not at higher risk (HR, 1.07; 95% CI, 0.86–1.34). However, women with both PTEN loss and PIK3CA mutation (n = 38) were at an increased risk of breast cancer-specific mortality (HR, 1.65; 95% CI, 0.83–3.26). Conclusions: In this large epidemiologic study, the PTEN-mortality association was more pronounced for ER-negative tumors, and the joint PTEN loss and PIK3CA mutation may be associated with worse prognosis. Impact: Further studies with a larger sample of ER-negative tumors are needed to replicate our findings and elucidate underlying mechanisms.

Background: We investigated the associations of postdiagnostic dietary glycemic index (GI), glycemic load (GL), insulin index (II), and insulin load (IL) with breast cancer–specific and all-cause mortality. Methods: Among 8,932 women with stage I–III breast cancer identified in the Nurses' Health Study (NHS; 1980–2010) and NHSII (1991–2011), we prospectively evaluated the associations between postdiagnostic GI, GL, II, and IL, and breast cancer–specific and all-cause mortality. Participants completed a validated food frequency questionnaire every 4 years after diagnosis. Results: During follow-up by 2014 in the NHS and 2015 in the NHSII, 2,523 deaths, including 1,071 from breast cancer, were documented. Higher postdiagnostic GL was associated with higher risk of both breast cancer–specific mortality [HRQ5vsQ1 = 1.33; 95% confidence interval (CI) = 1.09–1.63; Ptrend = 0.008] and all-cause mortality (HRQ5vsQ1 = 1.26; 95% CI = 1.10–1.45; Ptrend = 0.0006). Higher all-cause mortality was also observed with higher postdiagnostic GI (HRQ5vsQ1 = 1.23; 95% CI = 1.08–1.40; Ptrend = 0.001), II (HRQ5vsQ1 = 1.20; 95% CI = 1.04–1.38; Ptrend = 0.005), and IL (HRQ5vsQ1 = 1.23; 95% CI = 1.07–1.42; Ptrend = 0.0003). The associations were not modified by insulin receptor or estrogen receptor status of the tumor, or body mass index. Conclusions: We found that higher dietary GL, reflecting postprandial glucose response, after a breast cancer diagnosis was associated with higher risk of breast cancer–specific mortality. Higher dietary GI, GL, II, and IL after a breast cancer diagnosis were associated with higher risk of death from any cause. Impact: These results suggest that carbohydrate quantity and quality may be important in breast cancer prognosis. See related commentary by McTiernan, p. 252

Background: Achieving a healthy weight is recommended for all breast cancer survivors. Previous research on postdiagnosis weight change and mortality had conflicting results. Methods: We examined whether change in body weight in the 18 months following diagnosis is associated with overall and breast cancer–specific mortality in a cohort of n = 12,590 stage I–III breast cancer patients at Kaiser Permanente using multivariable-adjusted Cox regression models. Follow-up was from the date of the postdiagnosis weight at 18 months until death or June 2015 [median follow-up (range): 3 (0–9) years]. We divided follow-up into earlier (18–54 months) and later (>54 months) postdiagnosis periods. Results: Mean (SD) age-at-diagnosis was 59 (11) years. A total of 980 women died, 503 from breast cancer. Most women maintained weight within 5% of diagnosis body weight; weight loss and gain were equally common at 19% each. Compared with weight maintenance, large losses (≥10%) were associated with worse survival, with HRs and 95% confidence intervals (CI) for all-cause death of 2.63 (2.12–3.26) earlier and 1.60 (1.14–2.25) later in follow-up. Modest losses (>5%– Conclusion: Large postdiagnosis weight loss is associated with worse survival in both earlier and later postdiagnosis periods, independent of treatment and prognostic factors. Impact: Weight loss and gain are equally common after breast cancer, and weight loss is a consistent marker of mortality risk. Cancer Epidemiol Biomarkers Prev; 26(1); 44–50. ©2016 AACR. See all the articles in this CEBP Focus section, “The Obesity Paradox in Cancer: Evidence and New Directions.”

Preclinical studies support an anticancer effect of statin drugs, yet epidemiologic evidence remains inconsistent regarding their role in breast cancer primary prevention. Here, we report an updated analysis of the association between statin use and breast cancer incidence in the Nurses' Health Study (NHS) cohort. Postmenopausal NHS participants without a cancer history were followed from 2000 until 2012 (n = 79,518). Data on statin use were retrieved from biennial questionnaires. We fit Cox regression models to estimate associations between longitudinal statin use and breast cancer incidence. Over 823,086 person-years of follow-up, 3,055 cases of invasive breast cancer occurred. Compared with never users, both former and current statin users had similar rates of invasive breast cancer incidence [former users: HRadj, 0.96; 95% confidence interval (CI), 0.82–1.1; current users: HRadj, 1.1; 95% CI, 0.92–1.3]. Associations did not differ by estrogen receptor (ER) status or histology (ductal vs. lobular carcinoma). Statin use was not associated with risk of invasive breast cancer, irrespective of histologic subtype and ER status. Statin drugs do not appear to modify processes involved in breast cancer initiation. Cancer Epidemiol Biomarkers Prev; 25(1); 201–6. ©2016 AACR.

Background: Weight change after a breast cancer diagnosis has been linked to lower survival. To further understand effects of postdiagnostic weight variation on survival, we examined the relationship by comorbid status and initial body mass index (BMI). Methods: The current analysis included 12,915 patients with breast cancer diagnosed between 1990 and 2006 with stage I–III tumors from four prospective cohorts in the United States and China. HRs and 95% confidence intervals (CI) representing the associations of five weight change categories [within Results: Mean weight change was 1.6 kg. About 14.7% women lost and 34.7% gained weight. Weight stability in the early years postdiagnosis was associated with the lowest overall mortality risk. Weight loss ≥10% was related to a 40% increased risk of death (HR, 1.41; 95% CI, 1.14–1.75) in the United States and over three times the risk of death (HR, 3.25; 95% CI: 2.24, 4.73) in Shanghai. This association varied by prediagnosis BMI, and in the United States, lower survival was seen for women who lost weight and had comorbid conditions. Weight gain ≥10% was associated with a nonsignificant increased risk of death. Conclusions: Prevention of excessive weight gain is a valid public health goal for breast cancer survivors. Although intentionality of weight loss could not be determined, women with comorbid conditions may be particularly at risk of weight loss and mortality. Impact: Weight control strategies for breast cancer survivors should be personalized to the individual's medical history. Cancer Epidemiol Biomarkers Prev; 21(8); 1260–71. ©2012 AACR.

Background: Previous studies convincingly showed an increase in risk of breast cancer associated with current or recent use of oral contraceptives from the 1960s to 1980s. The relation of contemporary oral contraceptive formulations to breast cancer risk is less clear. Methods: We assessed lifetime oral contraceptive use and the specific formulations used among 116,608 female nurses ages 25 to 42 years at enrollment in 1989, and subsequently updated this information every 2 years. We related this information to risk of breast cancer up to June 1, 2001. Results: During 1,246,967 person-years of follow-up, 1,344 cases of invasive breast cancer were diagnosed. Past use of any oral contraceptive was not related to breast cancer risk [multivariate relative risk (RR), 1.12; 95% confidence interval 0.95-1.33]. Current use of any oral contraceptive was related to a marginally significant higher risk (multivariate RR, 1.33; 95% CI, 1.03-1.73). One specific formulation substantially accounted for the excess risk: the RR for current use of triphasic preparations with levonorgestrel as the progestin was 3.05 (95% CI, 2.00-4.66; P < 0.0001). Conclusions: Current use of oral contraceptives carries an excess risk of breast cancer. Levonorgestrel used in triphasic preparations may account for much of this elevation in risk. Impact: Different oral contraceptive formulations might convey different risks of breast cancer; ongoing monitoring of these associations is necessary as oral contraceptive formulations change. Cancer Epidemiol Biomarkers Prev; 19(10); 2496–502. ©2010 AACR.

Several lines of evidence suggest that vitamin D may reduce incidence of breast cancer, but few epidemiologic studies have addressed the relation of plasma vitamin D metabolites to the risk of this disease. We prospectively examined the relationship between plasma levels of 25-hydroxyvitamin D [25(OH)D] and 1,25-dihydroxyvitamin D [1,25(OH)2D] and risk of breast cancer in a case-control study nested within the Nurses' Health Study cohort. Blood samples were collected from study participants in 1989-1990. Breast cancer cases developing between blood collection and June 1, 1996, were matched to cancer-free controls on the basis of age, menopausal status, and other factors. Stored plasma samples from 701 cases and 724 controls were available for metabolite analysis. Cases had a lower mean 25(OH)D level than controls (P = 0.01), but mean 1,25(OH)2D levels were similar (P = 0.49). High levels of both metabolites were associated with a nonsignificant lower risk of breast cancer. Women in the highest quintile of 25(OH)D had a relative risk of 0.73 (95% confidence interval = 0.49-1.07; Ptrend = 0.06) compared with those in the lowest quintile. For 1,25(OH)2D, the comparable relative risk was 0.76 (95% confidence interval = 0.52-1.11; Ptrend = 0.39). For both metabolites, the association was stronger in women ages 60 years and older, but results were not statistically significant. Our findings suggest that high levels of 25(OH)D, and perhaps 1,25(OH)2D, may be modestly associated with reduced risk of breast cancer.