PDCD1 and cancer: Studies reported a positive correlation of CD8+-infiltrating lymphocytes and control of tumor growth.40 Additionally, the intratumoral presence of T cells expressing the integrin CD103 has been strongly correlated with favorable prognosis for patients with cancer,41 independently of the infiltration of CD8+ T cells.42 Moreover, TRM cell express immune checkpoint molecules, which may be a potential surrogate marker of response to immunotherapy as they could expand early during anti-PD-1 treatment.43