Parity improves anti-tumor immunity in breast cancer patients

Clustering of HR + /HER2- breast cancer in an Asian cohort is driven by immune phenotypes

Breast cancer exhibits significant heterogeneity, manifesting in various subtypes that are critical in guiding treatment decisions. This study aimed to investigate the existence of distinct subtypes of breast cancer within the Asian population, by analysing the transcriptomic profiles of 934 breast cancer patients from a Malaysian cohort. Our findings reveal that the HR + /HER2- breast cancer samples display a distinct clustering pattern based on immune phenotypes, rather than conforming to the conventional luminal A-luminal B paradigm previously reported in breast cancers from women of European descent. This suggests that the activation of the immune system may play a more important role in Asian HR + /HER2- breast cancer than has been previously recognized. Analysis of somatic mutations by whole exome sequencing showed that counter-intuitively, the cluster of HR + /HER2- samples exhibiting higher immune scores was associated with lower tumour mutational burden, lower homologous recombination deficiency scores, and fewer copy number aberrations, implicating the involvement of non-canonical tumour immune pathways. Further investigations are warranted to determine the underlying mechanisms of these pathways, with the potential to develop innovative immunotherapeutic approaches tailored to this specific patient population.

OUP accepted manuscript

Background

Methods

Results

Conclusion

Rethinking the carcinogenesis of breast cancer: The theory of breast cancer as a child deficiency disease or a pseudo semi-allograft

The theory of breast cancer as a child deficiency disease is an inversion of the current paradigm, which considers full-term pregnancies to be a protective factor and uses nulliparous women as the reference group. Instead, the theory of breast cancer as a child deficiency disease says that women with the highest parity (about 20, which is the limit of human fertility) are those with the lowest risk and should be used as the reference group in risk estimations. This theory is explained biologically by converting parity from the simple value of number of children into an understanding of the long-lasting biological and immunological effects of pregnancy. These effects can be reflected, as measured by functional genomics, in gene expression of the immune cells in the blood. Each pregnancy represents a unique fetus or semi-allograft, which provokes the creation and deposit of memory cell clones in the mother. Gene expression levels have been found to change linearly with number of full-term pregnancies in healthy women, but not in breast cancer patients. High hormone levels are necessary for a successful pregnancy, as they modulate the immune response from adaptive to innate in order to protect the fetus (considered as a semi-allograft) from rejection. At the end of the pregnancy, hormone levels drop, and the immune system recognizes the semi-allograft, but not in time for rejection to occur before birth. High hormones levels are also classified as carcinogens illustrating that carcinogenesis in the breast could be viewed as a war or balance between later exposures to hormonal carcinogens and the protection of the immune system. We propose that breast tumors are pseudo semi-allografts made up of transformed breast tissue cells. Assuming that the sensitivity to the exposure to increased levels of endogenous or exogenous hormones in women with breast cancer mimic those that occur in pregnancy, these breast tumor cells are protected against the body's immune reaction, just as the fetus is during pregnancy. However, with more pregnancies, the potential to eradicate the pseudo semi-allograft might increase due to enhanced immune surveillance. The theory of breast cancer as a child deficiency disease proposes that the protective effect of pregnancy on breast cancer incidence via the immune system is independent of other risk factors.

Each pregnancy linearly changes immune gene expression in the blood of healthy women compared with breast cancer patients

Background

There is a large body of evidence demonstrating long-lasting protective effect of each full-term pregnancy (FTP) on the development of breast cancer (BC) later in life, a phenomenon that could be related to both hormonal and immunological changes during pregnancies. In this work, we studied the pregnancy-associated differences in peripheral blood gene expression profiles between healthy women and women diagnosed with BC in a prospective design.

Methods

Using an integrated system epidemiology approach, we modeled BC incidence as a function of parity in the Norwegian Women and Cancer (NOWAC) cohort (165,000 women) and then tested the resulting mathematical model using gene expression profiles in blood in a nested case-control study (460 invasive case-control pairs) of women from the NOWAC postgenome cohort. Lastly, we undertook a gene set enrichment analysis for immunological gene sets.

Results

A linear trend fitted the dataset precisely showing an 8% decrease in risk of BC for each FTP, independent of stratification on other risk factors and lasting for decades after a woman's last FTP. Women with six children demonstrated 48% reduction in the incidence of BC compared to nulliparous. When we looked at gene expression, we found that 756 genes showed linear trends in cancer-free controls (false discovery rate [FDR] 5%), but this was not the case for any of the genes in BC cases. Gene set enrichment analysis of immunologic gene sets (C7 collection in Molecular Signatures Database) revealed 215 significantly enriched human gene sets (FDR 5%).

Conclusion

We found marked differences in gene expression and enrichment profiles of immunologic gene sets between BC cases and healthy controls, suggesting an important protective effect of the immune system on BC risk.