Late recurrence of breast cancer is associated with pro-cancerous immune microenvironment in the primary tumor.

The fact that 20-40% of all breast cancer (BC) patients develop recurrence when 5 year survival is 90% strongly suggests that late recurrence, i.e. more than 5 years after diagnosis, is the remaining challenge to decrease the absolute number of BC deaths. Better understanding late recurrence is an essential first step to address this issue. We hypothesized that primary tumors with a distinctive tumor immune microenvironment will develop late recurrence. Accordingly, we evaluated the relationship between the timing of cancer recurrence, clinical factors, gene expression profiles, and immune status utilizing two published large cohorts. 308 primary BCs in TCGA were analyzed and categorized as: recurrence ≤2 years (Early, n = 49), between 2-5 years (Mid, n = 54), recurrence >5 years (Late, n = 20), and no recurrence >5 years (Survivors, n = 185). 1,727 primary BCs in METABRIC were analyzed and categorized similarly: Early, n = 170; distant (D), n = 19; local (L), Mid, n = 213; D, n = 21; L, Late, n = 199; D, n = 57, L, and Survivors, n = 1048. Utilizing pre-ranked GSEA, we showed that primary tumors with Survivors were associated with anti-cancer signaling such as INF-α/-γ response and TNF-α signaling, compared with all recurrence groups in pre-ranked GSEA. Furtherrmore, we found that host defense immunity (leukocyte fraction, lymphocyte infiltration, and macrophage fractions) was decreased in primary tumors with Late recurrence compared with Survivors. Utilizing the CIBERSORT algorithm, we showed anti-cancer lymphocytes, memory CD4+ T cells and γδT cells, were significantly lower, and pro-cancerous regulatory T cells were significantly higher in Late tumors compared with Survivors. In agreement, cytolytic activity score that assesses immune cell cytolytic activity was significantly lower in Late compared with Survivors. We demonstrated that not only host defense immunity, but also pro-cancerous immune cells and immune cell cytolytic activity in primary BC was associated with late recurrence.