Histoprognostic grade is a determinant parameter to select the initial therapeutic strategy in breast cancer. Our aim was to analyze the grade repartition in BRCA1-associated breast cancer (BC) and to explore the possible connections between grade and the BRCA1 gene function. We first compared 27 BRCA1-associated BCs from 14 families with 4461 cases from an administrative district registry and 242 cases from a hospital-based registry, matching for grade and constitutive elements, and then considered their repartition in families.

We observed a prevalence of grade 3 (P < 0.0001) in BRCA1-associated BC. This was attributed mainly to nuclear polymorphism (P < 0.0001), mitotic activity (P < 0.0001), and tubular differentiation (P = 0.0004), implying that BRCA1-associated BCs are highly proliferating tumors. Moreover, it is suggested that grade segregates as a genetic trait within families (P = 0.0015), and this was attributed to the mitotic index segregation only (P = 0.0005). Therefore grade, through its components, could be interpreted as the morphological translation of the BRCA1 germ line mutation. Thus, a genotype-phenotype correlation may exist between the type of mutation and the aggressiveness of the disease.

These findings are bound to have an important impact in the care management of hereditary breast cancer at the individual and at the familial level and in the comprehensive approach of breast cancer development.

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This work was supported by Paoli-Calmettes Institute, INSERM, and grants from La Ligue Nationale Contre le Cancer (the National Office and the district committees of Alpes de Haute Provence, Bouches du Rhône, Corse du Sud, Haute Corse, Var), Caisse Nationale d'Assurance Maladie, CAMPLP, FEGEFLUC, Association pour la Recherche sur le Cancer, Fédération Nationale des Centres de Lutte Contre le Cancer, and Groupement de Recherche et d'Etude sur les Génomes.

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