Peritumoral eosinophils predict recurrence in colorectal cancer

In colorectal cancer, the presence and extent of eosinophil granulocyte infiltration may render important prognostic information. However, it remains unclear whether an increasing number of eosinophils might simply be linked to the overall inflammatory cell reaction or represent a self-contained, antitumoral mechanism that needs to be documented and promoted therapeutically. Peri- and intratumoral eosinophil counts were retrospectively assessed in 381 primary colorectal cancers from randomly selected patients. Tumors were diagnosed in American Joint Committee on Cancer (AJCC)/Union Internationale Contre le Cancer (UICC) stage I in 21%, stage II in 32%, stage III in 33%, and stage IV in 14%. Presence and extent of eosinophils was related to various histopathological parameters as well as patients' outcome. Overall, peri- and intratumoral eosinophils were observed in 86 and 75% cancer specimens. The peritumoral eosinophil count correlated strongly with the intratumoral eosinophil count (R=0.69; P<0.001) and with the intensity of the overall inflammatory cell reaction (R=0.318; P<0.001). Both increasing peri- and intratumoral eosinophil counts were significantly associated with lower T and N classification, better tumor differentiation, absence of vascular invasion, as well as improved progression-free and cancer-specific survival. However, only peritumoral eosinophils, but not intratumoral, were an independent prognosticator of favorable progression-free (hazard ratio 0.75; 95% confidence interval 0.58-0.98; P=0.04) and cancer-specific survival (hazard ratio 0.7; 95% confidence interval 0.52-0.93; P=0.01)-independent of the intensity of overall inflammatory cell reaction. This was also found for patients with AJCC/UICC stage II disease, wherein the presence of peritumoral eosinophils was significantly associated with favorable outcome. In conclusion, the number of peritumoral eosinophils had a significant favorable impact on prognosis of colorectal cancer patients independent of the overall tumor-associated inflammatory response. Evaluation of peritumoral eosinophils represents a promising readily assessable tool and should therefore routinely be commented on in the pathology report.