Figure 2. Evolution of mammary gland and pregnancy-associated TNBCs.

The different stages of parity (pregnancy, lactation and involution) super-imposed on the different events occurring. The proliferation and specification of the mammary gland occurs during pregnancy and seizes during lactation. In contrast, differentiation of these cells during lactation leads to their elimination by apoptosis during involution. It is proposed that the inflammatory environment associated with involution that induced normally after longer lactation periods would target terminally differentiated cells and kill them. In contrast, forced involution induced by lack or short duration of breastfeeding could lead to inflammatory environment that could promote the survival and expansion of less differentiated cells and formation of aggressive TNBCs/PACSs.