Postpartum breast cancer diagnosed during involution: a distinct entity with unique clinicopathological, molecular and immunological features?
Around 10-25% of breast cancers in young women are diagnosed during pregnancy or the postpartum years. Given the trend to delay childbearing, this frequency is expected to increase. Emerging evidence from our group and others indicates that breast cancers diagnosed in the postpartum period (PPBC) have a worse prognosis, with an increased risk for metastasis and death than breast cancers occurring during or outside pregnancy. The (immuno)biology of PPBC is poorly understood and, hence, it is unknown why PPBC has an enhanced risk for metastasis or how PPBC should be effectively targeted for improved survival. Studies, predominantly performed in rodents, postulated that the involution process of the mammary gland after pregnancy or/and lactation causes or contributes to the aggressive behavior of PPBC. However, evidence from human tissue is lacking. This project aims to elucidate whether PPBC, specifically diagnosed during mammary gland involution (PPBC-inv), is a distinct type of breast cancer, exhibiting unique molecular and immunological features compared to breast cancers diagnosed during and outside pregnancy. A genomewide transcriptome analysis as well as multiplex IHC will be applied on tumour biopsy tissue from a large PPBC-inv cohort and 2 control groups. The results from this pioneering scientific work may provide novel insights in pathways and genes affected in PPBC-inv and may point to novel (immuno)therapeutic targets for PPBC-inv.