MDK and nonpapillary renal cell carcinoma: Liu et al., through scRNA-seq, identified a subset of MCs in ccRCC characterized by high expression of procollagen-lysine 2-oxoglutarate 5-dioxygenase 2 (PLOD2) and serum amyloid A 1(SAA1), and significantly involved in initiating signaling pathways for SPP1, MIF, pleiotrophin (PTN), and midkine (MK).