RPP40 (ribonuclease P/MRP subunit p40) is a protein component of two essential ribonucleoprotein complexes involved in RNA processing. As part of ribonuclease P, RPP40 participates in generating mature tRNA molecules by cleaving their 5' leader sequences 1. RPP40 also functions within the ribonuclease MRP complex, which processes pre-rRNA and facilitates ribosomal RNA maturation through endonucleolytic cleavage of internal transcribed spacers 2. At the molecular level, RPP40 forms multiple weak protein-protein interactions with other RNase P subunits and directly interacts with the RNA component 34. Clinically, RPP40 has emerged as a disease-relevant biomarker. Elevated RPP40 expression correlates with poor outcomes in hepatocellular carcinoma (HCC), where it promotes cell proliferation, migration, and invasion by coordinating transcription of ribosomal genes 5. RPP40 is also included in a 7-mRNA prognostic signature for predicting recurrence risk in early-stage triple-negative breast cancer 6. Conversely, in systemic sclerosis, autoantibodies against RPP40 and other Th/To complex components show a protective effect against contemporaneous cancer development 7. These findings suggest RPP40 warrants investigation as both a therapeutic target and prognostic marker in malignancy.