Histologic characterization of stem cells in mammary epithelium and stroma

It is unknown whether native cells in benign breast tissue mediate risk of cancer.
We therefore aimed to identify cell types in benign human mammary tissue
immunohistologically using markers of stemness and differentiation, and to
investigate their possible associations with clinical risk factors for breast cancer.
We found that cells that are integrated in benign epithelium and are
immunoreactive for the stem cell marker ALDH1 are negative for markers of
glandular differentiation, proliferation, and estrogen receptor. High numbers of
these cells were associated with the risk factors family history of breast cancer,
BRCA1/2 carrier status, low parity, and hormone use.
Stromal ALDH1+ cells are either spindle-shaped/polygonal (s/p) or round/oval
(r/o), and the latter are positive for the contractile protein marker SMMHC.
ALDH1+ s/p cells are positive for the stellate cell marker vinculin. Low numbers
of these cells were associated with family history, and when negative for the stem
cell marker CD44 they were associated with nulliparity. Low numbers of
ALDH1+ CD44+ CD24– r/o cells were associated with family history. ALDH1+
r/o cells were positively or negatively associated with low parity depending on the
patients' BRCA1/2 status.
High numbers of r/o cells that are positive for the mesenchymal stem cell
marker SSEA3 were associated with low parity, family history, and hormone use
after menopause.
This study describes novel stromal cells in breast that were associated with risk
factors for breast cancer. If confirmed in independent cohorts, they may be used
for stratification of women with regard to risk of breast cancer.