Project Title: “Tamoxifen reverses the hyperplastic changes induced by abrupt involution in mouse mammary glands”
Mentor: Bhuvaneswari Ramaswamy, Internal Medicine
Background: Epidemiological data links lack of breastfeeding with increased risk for breast cancer(BC)1. During pregnancy, the mammary epithelium undergoes lobuloalveolar differentiation to produce milk. Post-lactation, breasts involute (with cell death) to near pre-pregnant stage. Extended breastfeeding(>6 months) allows gradual involution(GI), whereas lack/short period of breastfeeding(< 3 months) causes abrupt involution(AI). We modeled GI vs. AI in mice. AI led to increased estrogen signaling followed by ductal hyperplasia, increased cell proliferation, chronic inflammation and expansion of luminal progenitor (LP) population, putative origin for basal-like BC; indicating pro-tumorigenic changes2. We hypothesize that treatment with anti-estrogen tamoxifen will mitigate AI effects and potentially act as preventive treatment to reduce BC risk in women who cannot breastfeed.
Methods: Wild-type FVB/N mice (8-weeks) were mated and normalized to 6pups/dam at partum. To induce AI, pups were weaned d7PP(postpartum). Tamoxifen treatment was initiated by implanting 5mg sustained release (60day or 21day) pellet on d8, d15, or d35PP, or placebo (control) in subscapular region. Mammary glands were harvested d28 and d120PP. FFPE sections and immunohistochemistry were used to evaluate histology, cell proliferation and collagen deposition. Flow cytometry of single-cell suspension was used to evaluate mammary epithelial subpopulation. Mammary total RNA was subjected to Affymetrix and Gene set enrichment analysis(GSEA).
Results: Sixty day tamoxifen treatment initiated d8, d15, or d35PP abrogated hyperplasia in AI glands. Treatment initiated on d8PP for 21days nearly abrogated hyperplasia. Tamoxifen treatment markedly reduced cell proliferation, collagen deposition and LP population. GSEA revealed de-enrichment of estrogen signaling, marked reduction of Elf5 (LP marker), Cdh1, Epcam expression and increased expression of serine protease Klk1 necessary for involution, S100A8&9, Mmd2 and Gadd45b.
Conclusion: Increased estrogen signaling is a key aberration observed in abruptly involuted mammary glands leading to precancerous changes. Our data revealed tamoxifen treatment postpartum prevented development of hyperplasia, reduced cell proliferation, collagen deposition and LP population, potentially reducing BC risk. Gene expression data revealed potential role of Elf5 promoting precancerous changes in AI and Klk1, Mmd2, S100A8/9 in mitigating negative AI impact. Our study reveals tamoxifen has potential as a prophylactic treatment to reduce BC risk for women unable to breastfeed.
- PMID12133652 2. PMID31315645
Keywords: breast cancer, abrupt involution, tamoxifen
Poster: AURF 2020- Mawalkar