Eosinophilia is a favorable prognostic marker for oral cavity and lip squamous cell carcinoma.

Eosinophils are frequently encountered with squamous cell carcinomas (SCC) and it has been proposed that tumor-associated tissue eosinophilia (TATE) could be of prognostic significance in oral SCC. The aim was to evaluate TATE in 83 oral cavity and 16 lip SCCs as well as the best possible use of TATE as a prognostic marker. The number of eosinophils was counted per high power fields (HPF, ×400) in three different representative areas of the tumor and its stroma. The degree of TATE was analyzed in relation to clinicopathological features of tumors and patients' survival (follow-up mean 40.7 months) using Fisher's exact test. TATE was detected in 58 (70%) oral and 8 (50%) lip SCC samples. The median number of eosinophils between oral and lip SCC was different (p = 0.028) but TATE was similar per HPF (p = 0.085). Totally, 6% of lip and 21% of oral SCC patients died during the follow-up. The patients with the higher TATE had significantly better survival than the patients with the lower TATE (p = 0.0136). The best cut-off value predicting the survival was 4 eosinophils/HPF. TATE is a prognostic marker for oral and lip SCC: more than 4 eosinophils/HPF may predict more favorable prognosis.