PDCD1 and metastatic melanoma: It is especially essential to accurately recognize the bacterial species that predispose to the development of a lower response to immunotherapy or adverse events and specific probiotics, which can selectively be administered to improve clinical responses. In conclusion, the modulation of the GM, particularly with FMT, emerges as a fascinating therapeutic tool in the treatment of patients with anti-PD-1 refractory metastatic melanoma, and this greater propagation of knowledge about the relationship between the GM and the immune system lets us hope for the best in the near future.