New Delhi, March 31 Scientists have developed a detailed map of breast tissue that shows that as women age, cells decline and multiply less, thereby creating a 'micro-environment' where cancer cells can thrive.
The map, described in a paper in the journal Nature Aging, helps explain why breast cancer risk increases with age and why tumors in younger women differ biologically.
"Even though breast cancer affects over two million women worldwide, we understand very little about why and when it occurs," said first author Pulkit Gupta, from the Cancer Research UK Cambridge Institute at the University of Cambridge.
"As cells divide and replicate, they accumulate mutations that can drive cancer, but why is it that the body can get rid of these mutated cells when we're younger, but struggles later in life?" Gupta said.
Breast cancer is the most common form of cancer to affect women, with about 80 per cent of cases occurring in women aged 50 and above, and the chances of developing an invasive breast cancer increasing with age.
The researchers analysed breast tissue from more than 500 women aged 15 to 86 using imaging techniques. The tissue samples included biopsies taken for non-cancer-related reasons.
Combining the images with details of hormone receptors, immune cells and tissue architecture, the researchers were able to map how breast tissue changes over time in unprecedented detail.
"Using imaging mass cytometry to profile the spatial expression of 40 proteins, we explore age-related remodelling of normal breast tissues in over 3 million cells from 527 reduction mammoplasties," the authors wrote.
"Aged breast tissue was less cellular and less proliferative for all cell types (epithelial, stromal and immune)," they said.
The researchers found that aging tissue has fewer cells and divide far less often. Milk-producing lobules shrink or disappear, ducts become more prominent with thicker supporting layers, fat cells increase, and blood vessels decrease.
Gupta said, "Our map revealed that as women age, their breast tissue goes through major changes, with the most dramatic changes occurring at menopause. There are also changes during their twenties, possibly linked to pregnancy and childbirth, but these are far less pronounced."
Describing changes in the immune environment, the researchers said younger breasts have more B cells and active T cells -- both are types of immune cells -- which helps them identify and kill cancer cells.
As breast tissue ages, the cells decline in number and are replaced by other types of immune cell indicating a more inflammatory and potentially less protective immune environment, the team said.
Further, cells in the breast tissue grow farther from each other and interact less -- immune and stromal cells (create a tissue 'scaffold') distance themselves from epithelial cells, which line the mammary ducts and lobules, thereby making it easier for pre-cancerous cells to escape control, the researchers said.