I think it is the bad eating habits of pregnant women during pregnancy, and the poor physical condition of pregnant women themselves, the lack of nutrition to supply themselves and the fetus, resulting in dystocia caused by too heavy body load during pregnancy, resulting in death.

https://www.cd-genomics.com/Human-Whole-Genome-PacBio-SMRT-Sequencing.html

I have heard a news that scientist dissected human breast epithelial cells and identified three epithelial cell populations. The discovery of these new cells helps redefine the origin of breast cancer, improve early cancer detection, slow cancer progression, and possibly even prevent cancer. In this study, the researchers utilized a next-generation sequencing technology combined with single cell RNA sequencing (Single cell RNA seq)to create a high-resolution molecular screening of human breast epithelial cells. Single-cell RNAseq technology has led to the discovery of cellular differences that have not been previously discovered.
Breast cancer arises from the breast epithelium. Breast cancer arises from genetic variation of breast epithelial cells. Genetic changes cause cancer cells of the breast tissue to produce canceration. Understanding the early origin of breast cancer has the potential to be transformed into an early diagnosis method for cancer, and to build a first line of defense against cancer before the disease threatens life. Maybe with the fast development of science technology, people will able to cure this disease completely.More information on the web :https://www.cd-genomics.com/single-cell-rna-sequencing.html