Poor Outcome in Postpartum Breast Cancer Patients Is Associated with Distinct Molecular and Immunologic Features

Area of Science:

• Oncology
• Immunology
• Breast Cancer Research

Background:

• Postpartum breast cancer diagnosed after breastfeeding cessation (PP-BCPW) shows a worse prognosis than other breast cancer types.
• Mammary gland involution is implicated in stimulating tumor growth, but molecular mechanisms in PP-BCPW are poorly understood.

Purpose of the Study:

• To investigate distinct prognostic features in postpartum breast cancer tumor tissue.
• To explore the role of mammary gland involution, using the postweaning period as a surrogate, in PP-BCPW.

Main Methods:

• Whole transcriptome sequencing, immunohistochemistry, and multiplex immunofluorescence were performed on tumor tissues.
• Patient groups included PP-BCPW, postpartum breast cancer during lactation (PP-BCDL), pregnant (Pr-BC), and nulliparous (NP-BC) patients.

Main Results:

• PP-BCPW patients with low immunoglobulin gene signature expression and high plasma B cell infiltration showed increased risk of metastasis and death.
• Increased CD8+ cytotoxic T cells and reduced cell distances were observed in PP-BCPW tumors but did not correlate with clinical outcomes.

Conclusions:

• Plasma B cells are crucial in the postweaning mammary tumor microenvironment, contributing to the poor prognosis of PP-BCPW.
• Further research into B-cell immunobiology is needed for this patient group.