Tumor-infiltrating lymphocytes in ipsilateral breast tumor recurrences predict prognosis

546 Background: The antitumoral immune response is dynamic and changes with tumor progression. Previous studies show that immunohistochemical (IHC) assessment of TILs in local recurrences can predict prognosis. It is not clear how adjuvant radiotherapy (RT) can alter the local immune response or if gene expression analyses of TILs in recurrences can provide prognostic information. Methods: Matched biopsies from primary tumors and ipsilateral breast tumor recurrences (IBTRs) from the randomized SweBCG91RT trial were assessed for TILs. Analyses were performed using gene expression (86 matched pairs) and IHC assessment (126 matched pairs). Results: The median time to IBTR was 8.0 years among irradiated patients and 3.6 years among unirradiated patients. In the gene expression analyses, higher absolute values of CD8+ T cells, CD4+ effector memory and CD8+ effector memory T cells in the recurrence could significantly predict a decreased risk of subsequent distant metastasis. In addition, a net increase of these cells in the IBTR compared to the primary tumor was associated with a significantly lower risk of metastasis. TILs did not change significantly between the matched tumors for the whole group or among irradiated patients versus unirradiated patients in the gene expression or IHC analyses. Surprisingly, the group with unchanged TILs levels as measured by IHC had the lowest risk of metastasis while an increase or a decrease in TILs was significantly associated with an increased risk. Conclusions: Cytotoxic and memory T cells in the recurrence protect against subsequent distant metastasis although IHC measurement of TILs could not confirm these results. No significant differences in TILs infiltration between irradiated versus unirradiated patients could be determined in the recurrences. Further analyses including changes of subtypes between the primary tumor and the recurrence will be presented.