Breast feeding, parity and breast cancer subtypes in a Spanish cohort.
BACKGROUND
Differences in the incidence and outcome of breast cancer among Hispanic women compared with white women are well documented and are likely explained by ethnic differences in genetic composition, lifestyle, or environmental exposures.  METHODOLGY/PRINCIPAL FINDINGS: A population-based study was conducted in Galicia, Spain. A total of 510 women diagnosed with operable invasive breast cancer between 1997 and 2010 participated in the study. Data on demographics, breast cancer risk factors, and clinico-pathological characteristics were collected. The different breast cancer tumor subtypes were compared on their clinico-pathological characteristics and risk factor profiles, particularly reproductive variables and breastfeeding. Among the 501 breast cancer patients (with known ER and PR receptors), 85% were ER+/PR+ and 15% were ER-&PR-. Among the 405 breast cancer with known ER, PR and HER2 status, 71% were ER+/PR+/HER2- (luminal A), 14% were ER+/PR+/HER2+ (luminal B), 10% were ER-/PR-/HER2- (triple negative breast cancer, TNBC), and 5% were ER-/PR-/HER2+ (non-luminal). A lifetime breastfeeding period equal to or longer than 7 months was less frequent in case patients with TNBC (OR = 0.25, 95% CI = 0.08-0.68) compared to luminal A breast cancers. Both a low (2 or fewer pregnancies) and a high (3-4 pregnancies) number of pregnancies combined with a long breastfeeding period were associated with reduced odds of TNBC compared with luminal A breast cancer, although the association seemed to be slightly more pronounced among women with a low number of pregnancies (OR = 0.09, 95% CI = 0.005-0.54).


CONCLUSIONS
In case-case analyses with the luminal A cases as the reference group, we observed a lower proportion of TNBC among women who breastfed 7 or more months. The combination of longer breastfeeding duration and lower parity seemed to further reduce the odds of having a TNBC compared to a luminal A breast cancer.
Oncology and Genetics Unit, Genomic Medicine Group, Complejo Hospitalario Universitario de Vigo, Vigo, Spain. carmen.redondo.marey@sergas.es
Carmen M
CM
Redondo
Manuela
M
Gago-Domínguez
Sara Miranda
SM
Ponte
Manuel Enguix
ME
Castelo
Xuejuan
X
Jiang
Ana Alonso
AA
García
Maite Peña
MP
Fernández
María Ausencia
MA
Tomé
Máximo
M
Fraga
Francisco
F
Gude
María Elena
ME
Martínez
Víctor Muñoz
VM
Garzón
Ángel
Á
Carracedo
J Esteban
JE
Castelao
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001942:Breast Feeding; D001943:Breast Neoplasms / Q000145:classification / Q000453:epidemiology*; D005260:Female; D006801:Humans; D008875:Middle Aged; D010298:Parity; D011247:Pregnancy; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism; D011960:Receptors, Estrogen / Q000378:metabolism; D011980:Receptors, Progesterone / Q000378:metabolism; D012307:Risk Factors; D013030:Spain / Q000453:epidemiology; D044465:White People
D018719:Erb-b2 Receptor Tyrosine Kinases; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone