Parity and the risk of breast and ovarian cancer in BRCA1 and BRCA2 mutation carriers.
Environmental or lifestyle factors are likely to explain part of the heterogeneity in breast and ovarian cancer risk among BRCA1 and BRCA2 mutation carriers. We assessed parity as a risk modifier in 515 and 503 Spanish female carriers of mutations in BRCA1 and BRCA2, respectively. Hazard ratios (HR) and their corresponding 95% confidence intervals (CI) were estimated using weighted Cox proportional hazards regression, adjusted for year of birth and study centre. The results for ever being parous and number of live-births were very similar for carriers of mutations in both genes. For all mutation carriers combined, the estimated HR associated with ever having had a live-birth was 0.74 (95% confidence interval [CI] = 0.55-1.01, P = 0.06), and that associated with each live-birth was 0.87 (95%CI = 0.77-0.98, P = 0.02). The latter association was observed only in women aged 40 and above (HR = 0.81, 95%CI = 0.70-0.94, P = 0.004 vs. HR = 0.99, 95%CI = 0.83-1.18, P = 0.9 for women under age 40), and this trend was highly consistently observed for carriers of mutations in each gene. There was no evidence of an association between breast cancer risk and age at first birth for parous BRCA1 or BRCA2 mutation carriers (P-trend >or= 0.3). The power to detect associations with ovarian cancer risk was much lower, especially for BRCA2 mutation carriers. Nevertheless, having a live-birth was associated with protection for BRCA1 mutation carriers (HR = 0.41, 95%CI = 0.18-0.94, P = 0.03), and a strong and consistent protective effect of age at first birth was observed for parous carriers of mutations in both genes (HR = 0.65, 95%CI = 0.52-0.83, P < 0.001). This is the third independent study to find that, as in the general population, parity appears to be associated with protection from breast cancer in women with mutations in BRCA1 and BRCA2. Parity appears to be protective for ovarian cancer in BRCA1 mutation carriers, but its role in BRCA2 mutation carriers remains unclear. Whether later age at first birth is also protective for ovarian cancer in mutation carriers requires further confirmation.
Grupo de Epidemiología Genética y Molecular, Programa de Genética del Cáncer Humano, Centro Nacional de Investigaciones Oncológicas (CNIO), C/Melchor Fernández Almagro, Madrid, Spain. rmilne@cnio.es
Roger L
RL
Milne
Ana
A
Osorio
Teresa
T
Ramón y Cajal
Montserrat
M
Baiget
Adriana
A
Lasa
Eduardo
E
Diaz-Rubio
Miguel
M
de la Hoya
Trinidad
T
Caldés
Alex
A
Teulé
Conxi
C
Lázaro
Ignacio
I
Blanco
Judith
J
Balmaña
Gessamí
G
Sánchez-Ollé
Ana
A
Vega
Ana
A
Blanco
Isabel
I
Chirivella
Eva
E
Esteban Cardeñosa
Mercedes
M
Durán
Eladio
E
Velasco
Eduardo
E
Martínez de Dueñas
María-Isabel
MI
Tejada
María-Dolores
MD
Miramar
María-Teresa
MT
Calvo
Carmen
C
Guillén-Ponce
Raquel
R
Salazar
Carlos
C
San Román
Miguel
M
Urioste
Javier
J
Benítez
D000293:Adolescent; D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000235:genetics*; D004252:DNA Mutational Analysis; D005260:Female; D019398:Genes, BRCA1; D024522:Genes, BRCA2; D006579:Heterozygote; D006801:Humans; D008423:Maternal Age; D008875:Middle Aged; D009154:Mutation; D010051:Ovarian Neoplasms / Q000235:genetics*; D010298:Parity; D011247:Pregnancy; D012306:Risk