LAUSR

Breast cancer diagnosed during pregnancy (BCP) is a rare and highly challenging disease. To investigate the impact of pregnancy on the biology of breast cancer, we conducted a comparative analysis of a cohort of BCP patients and non-pregnant control patients by integrating gene expression, copy number alterations and whole genome sequencing data. We showed that BCP exhibit unique molecular characteristics including an enrichment of non-silent mutations, a higher frequency of mutations in mucin gene family and an enrichment of mismatch repair deficiency mutational signature. This provides important insights into the biology of BCP and suggests that these features may be implicated in promoting tumor progression during pregnancy. In addition, it provides an unprecedented resource for further understanding the biology of breast cancer in young women and how pregnancy could modulate tumor biology.Genetics: pregnancy-associated breast cancer shows altered mutational landscapeBreast cancers diagnosed during pregnancy exhibit unique molecular characteristics that could explain their aggressive nature. Christos Sotiriou from the Jules Bordet Institute in Brussels, Belgium, and colleagues compared the molecular and genetic profiles of tumors from women diagnosed while pregnant with those from age-matched, non-pregnant controls. Although genome-wide copy number alterations were similar in the two groups, tumors from patients diagnosed during pregnancy harbored a greater number of protein-altering gene mutations on average. Mutations were especially common in genes encoding mucins, a group of proteins involved in cancer progression. Pregnant patients were also associated with a mutational signature linked to mismatch repair deficiency. These results point to ways in which pregnancy may modulate tumor biology. The high mutational load found in women diagnosed during pregnancy also suggests these patients may be good candidates for immunotherapy.