Common wound healing signature in murine and human involuting breast, implications for pregnancy-associated breast cancer.

Abstract #1049 Full term pregnancy increases breast cancer risk for up to ten years after childbirth and breast cancer diagnosed during this time has been referred to as pregnancy associated breast cancer (PABC). PABC patients have high rates of metastasis, which is independent of known prognostic factors. Following parturition or lactation, during involution, the breast returns to its pre-pregnant state and in the rat model, we found mammary gland involution employs tissue remodeling programs activated during wound healing and inflammation including high matrix metalloproteinase -2, -3, and -9 activities, release of bioactive fragments of FN and LN, deposition of fibrillar collagen, and increased cytokine levels, including TGFβ1, TGFβ3 and CTGF. We hypothesize that this physiologically normal, but pro-inflammatory remodeling of the gland accounts for the high rate of metastases seen in PABC. To further define involution features common to wound healing that may account for the metastasis promoting attributes of PABC, the question of whether macrophages are recruited to the involuting gland was investigated in both rat mammary and human breast tissue. Using the macrophage marker CD68, a lysosomal associated protein, the number of CD68 positive cells in rat mammary glands increased more than 6 fold during involution. Involution-associated macrophages were identified as subtype M2-like by arginase-1 expression and lack of subtype M1-marker iNOS expression. To address the question of whether breast involution in women also is characterized by a wound-healing signature, formalin fixed breast biopsy tissues were obtained for women who were either pregnant, lactating, or whose breast tissue was actively involuting at the time of biopsy. Using a novel computer assisted imaging program, over 200 images of human breast tissue have been quantitated for CD68. CD68 staining in the human breast followed the same trend as in rat, with 5 times more staining in involuting compared to pregnant or lactating tissue. Total leukocyte number, as assessed by CD45 antibody, and oncofetal ECM protein tenascin-C staining were also increased in involuting human breast tissue. With respect to these three stromal markers, involuting human breast tissue was more similar to breast cancer stroma (N=50 images) than stroma from breasts of nulliparous women (N=30 images). These data demonstrate for the first time that human mammary gland involution is characterized by a pro-inflammatory microenvironment, implicating physiologic tissue inflammation in the poor prognosis of PABC. In a newly developed animal model for PABC, MCF10DCIS cells were injected orthotopically into SCID mice whose mammary glands were either quiescent (virgin mice) or actively remodeling following weaning (involuting mice). Tumor incidence was 78% in involuting and 50% in virgin mice. Further, tumor multiplicity, size and DCIS conversion to locally invasive lesions were significantly higher in the involuting mice than control virgin mice. This model is being utilized for mechanistic and chemopreventive studies of PABC. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 1049.