Studies have demonstrated arginase-1 expression in 0–7% of prostate cancer [25,26,27], 6% of adenocarcinomas of the ampulla Vateri [28], 84% of squamous cell carcinoma of the oral cavity and the larynx [14], and “high” expression in 47% of the 79 analyzed invasive breast carcinomas of no special type (NST) [29]. Here, ARG1 is linked to squamous cell carcinoma.