Tumor immune environment in multiple primary malignancies involving colorectal cancers: Comparison with single primary colorectal cancers

e15536 Background: Multiple primary malignancies (MPM) are characterized by two or more primary tumors in an individual patient, excluding relapse or subordinate relationship. Because the therapeutic options usually become limited, the diagnosis of MPM cause a lot of troubles to both clinicians and patients. A comprehensive investigation in comparing the tumor immune environment in MPM involving colorectal cancers (CRC) with single primary CRC will provide clues for the etiology and the management of MPM. Methods: Three patients with MPM involving CRC and twenty four patients with single primary CRC from our hospital were enrolled in the study. FFPE samples from colorectal lesions were analyzed for the tumor infiltrating lymphocytes [PD-L1+, PD-1+, CD3+, CD4+, CD8+, CD20+, FoxP3+, CD56+, CD163+, CD68+] by multiplex immunofluorescence technique. The tumor-enriched segments and stroma areas annotated by pathologists on images. Then artificial intelligence (AI) employing algorithms of image processing, machine learning, and deep learning techniques distinguished the core and peritumor areas, and calculated the density (counts per mm2) of each marker in two regions. A nonparametric approach (Kruskal–Wallis) was used to compare the density of immune cells between MPM involving CRC and single primary CRC groups. Results: The density of CD4+, CD56 dim , FoxP3+ cells in patients with single primary CRC were significantly higher than those in MPM both in the stroma and tumor-enriched segments (all, p < 0.05). In the tumor-enriched segments, the density of PD-1+ in patients with single primary CRC was also significantly more than that in MPM. Moreover, the density of PD-1+CD8+ cells in patients with single primary CRC showed a trend of higher density than those in MPM patients in the stroma area (p = 0.06). However, the density of PD-1+ and PD-1+CD8+ cells did not show significant differences related to cancer types (MPM and single primary CRC) in the stroma. Other indicators such as CD3+, CD20+, CD8+, CD68+CD163+, CD68+CD163-, CD56 bright and PD-L1+, had no significant difference related to cancer types (MPM and single primary CRC) regardless of the area (tumor-enriched segments and stroma area). Conclusions: We identified that the tumor infiltrating lymphocytes such as CD4+ cells infiltrated more in single primary CRC than those in MPM involving CRC, suggesting that MPM involving CRC may unresponsive to immunotherapy monotherapy. With preclinical studies suggesting potential for synergistic effects, combining immunotherapies may be a promising approach to treat MPM, which requires a further validation with a larger sample size.