Recreational physical activity and risk of triple negative breast cancer in the California Teachers Study.
Evidence has accumulated showing that recreational physical activity reduces breast cancer risk. However, it is unclear whether risk reduction pertains to specific receptor-defined subtypes. Moreover, few studies have examined whether changes in the amount of recreational physical activity during adulthood influence breast cancer risk.



A total of 108,907 women, ages 22 to 79 years with no history of breast cancer when joining the California Teachers Study in 1995-1996, completed a baseline questionnaire and were eligible for the study. Through 2012, 5882 women were diagnosed with invasive breast cancer. Breast cancer subtypes were defined by the expression status of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). Multivariable Cox proportional hazards models provided adjusted hazard ratios (HRs) and 95 % confidence intervals (CIs) for breast cancer overall and ER/PR/HER2-defined subtypes associated with long-term (from high school through age 54 or age at cohort entry, whichever was younger) and baseline (during 3 years prior to baseline) recreational physical activity. Among women who also completed a follow-up questionnaire at 10 years after baseline in 2005-2008 (54,686 women, 1406 with invasive breast cancer), risk associated with changes in the amount of recreational physical activity from baseline to the 10-year follow-up (during 3 years prior to the 10-year follow-up) was determined.



Both long-term and baseline strenuous recreational physical activity were inversely associated with risk of invasive breast cancer (P trend ≤0.03). The observed associations were mainly confined to women with triple negative breast cancer (TNBC, ER-/PR-/HER2-, P trend ≤0.02) or luminal A-like subtype (ER+ or PR+ plus HER2-) who were former users of menopausal hormone therapy at baseline (P trend = 0.02, P homogeneity of trends ≤0.03). Moreover, women who consistently engaged in the highest level (≥3.51 h/wk/y) of strenuous recreational physical activity between baseline and 10-year follow-up had the lowest risk of breast cancer (HR = 0.71, 95 % CI = 0.52-0.98) when compared to those who were consistently low (≤0.50 h/wk/y).



Strenuous recreational physical activity is associated with lower breast cancer risk, especially TNBC. The benefit may be maximized by consistently engaging in high-intensity recreational physical activity during adulthood.
Department of Population Sciences, Beckman Research Institute of City of Hope, 1500 East Duarte Road, Duarte, CA, 91010, USA. hma@coh.org.
Huiyan
H
Ma
Department of Population Sciences, Beckman Research Institute of City of Hope, 1500 East Duarte Road, Duarte, CA, 91010, USA.
Xinxin
X
Xu
Department of Population Sciences, Beckman Research Institute of City of Hope, 1500 East Duarte Road, Duarte, CA, 91010, USA.
Jessica
J
Clague
Department of Population Sciences, Beckman Research Institute of City of Hope, 1500 East Duarte Road, Duarte, CA, 91010, USA.
Yani
Y
Lu
Department of Population Sciences, Beckman Research Institute of City of Hope, 1500 East Duarte Road, Duarte, CA, 91010, USA.|Section of Environment and Radiation, International Agency for Research on Cancer, 150 Cours Albert Thomas, 69372, Lyon, France.
Kayo
K
Togawa
Department of Population Sciences, Beckman Research Institute of City of Hope, 1500 East Duarte Road, Duarte, CA, 91010, USA.
Sophia S
SS
Wang
Cancer Prevention Institute of California, 2201 Walnut Avenue, Fremont, CA, 94538, USA.
Christina A
CA
Clarke
Department of Preventive Medicine, Keck School of Medicine, University of Southern California, 2001 N Soto Street, Los Angeles, CA, 90032, USA.
Eunjung
E
Lee
Department of Epidemiology, School of Medicine, University of California, Irvine, 224 Irvine Hall, Irvine, CA, 92697, USA.
Hannah L
HL
Park
Department of Population Sciences, Beckman Research Institute of City of Hope, 1500 East Duarte Road, Duarte, CA, 91010, USA.
Jane
J
Sullivan-Halley
Department of Population Sciences, Beckman Research Institute of City of Hope, 1500 East Duarte Road, Duarte, CA, 91010, USA.
Susan L
SL
Neuhausen
Department of Population Sciences, Beckman Research Institute of City of Hope, 1500 East Duarte Road, Duarte, CA, 91010, USA.
Leslie
L
Bernstein
D015992:Body Mass Index; D002140:California / Q000453:epidemiology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D009043:Motor Activity; D009361:Neoplasm Invasiveness; D011159:Population Surveillance; D016016:Proportional Hazards Models; D011998:Recreation; D012306:Risk; D000070777:School Teachers; D064726:Triple Negative Breast Neoplasms / Q000453:epidemiology* / Q000209:etiology* / Q000473:pathology
BMI; Breast cancer; Estrogen receptor; HER2; Luminal; Menopausal hormone therapy; Physical activity; Progesterone receptor; Risk factors; Triple negative breast cancer