Targeted Prevention of Postpartum-Related Breast Cancer (PRBC)

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Postpartum-related breast cancers (PRBCs), herein defined as breast cancers (BCs) diagnosed within five years after a birth, augur a poor prognosis. Although early age at first birth and multiparity lower risk of late onset BCs, childbirth transiently increases risks of both estrogen receptor (ER)+ and ER- BCs for over two decades, with peak risks at 5 years postpartum (parous vs. nulliparous: HR=1.80, 95%CI=1.63-1.99). Peak risks are even higher among women with a family history of BC (parous vs. nulliparous: HR=3.53, 95%CI=2.91-4.29), and for women whose first birth is at later ages (pinteraction=0.03). In preclinical models, post-partum involution (PPI), a pro-inflammatory process which restores the breast to a non-lactating state after weaning, is linked to activation of cyclooxygenase-2 (COX-2), which increases production of prostaglandins and results in an immune suppressed, pro-carcinogenic “wound healing” microenvironment that drives BC progression; in these models, treatment with non-steroidal anti-inflammatory agents (NSAIDs) inhibits PRBC development. Among women, both postpartum normal breast tissues and BBD biopsies are characterized by significant inflammation. We and others have reported significantly reduced risk of BC among NSAID users with benign breast disease (BBD), suggesting a potential preventive benefit for women at risk of PRBC. We propose 3 aims to test the hypothesis that dysregulated PPI increases risk of BBD and PRBC, and that inhibition of deleterious inflammation following PPI can lower BC risk. In Aim 1, we will define and validate a PPI-specific immune signature score to distinguish normal breast tissues of young nulliparous from parous women (obtained within 5 years of a birth, matched by age) using 240 samples donated to the Komen Tissue Bank (KTB). We will also measure eicosanoids, including prostaglandin E2, in frozen tissues from a subset (n=100) of these women. We will define factors related to PPI immune signature score, hypothesizing that higher scores may indicate increased PRBC risk. In Aim 2, we will refine and independently test whether a PRBC immune signature score based on 8 previously defined markers with a combined AUC=0.76 predicts risk in previously untested BBD biopsies (75 cases and 75 matched controls). We will compare PRBC immune signature scores in 707 BCs from women aged 40 years or less by parity status, molecular subtype, and adjusted for potential confounders. In Aim 3, we will conduct a window of opportunity clinical trial to test if a 6-week course of aspirin 81 mg per day can reduce the deleterious inflammation associated with PRBC risk (i.e., PRBC immune score) and favorably alter other BC risk markers in breast tissues, blood and urine. This significant and innovative proposal seeks to define a unifying mechanism of pathogenesis for PRBC, which will provide the basis for developing a short-term, well-tolerated prevention strategy using immune-targeting and/or anti-inflammatory agents to prevent BC.