IDO1 and cutaneous melanoma: First, in contrast to data described by Krähenbühl et al. (16), who analyzed different primary cutaneous melanoma types and corresponding organ metastases (with exception of CNS metastases) in 43 patients undergoing cancer immunotherapy or targeted therapy and described IDO immunoreactivity in 17/43 pretreated samples, we found that IDO expression is highly consistant indicating IDO as a marker of anti-tumor immune response.