The enrichment of immunologic markers suggestive of an exhausted immune response including TGF-β-related signatures and several regulatory T-cell markers (IL10RA, IL10RB, HLA-DRA) as well as immune checkpoints (Tim-3, BTLA, CTLA-4, CD80, ICOS) provides strong immunobiologic foundations to justify the relationship between PD-L2 expression and poorer prognosis in patients with PCC/PGL. The gene discussed is ICOS; the disease is adrenal gland pheochromocytoma.