PPI network analysis of overlapping genes between RA and HNC revealed a moderately dense and cohesive network of 35 genes (ANGPT2, BTK, CCL19, CCL2, CCL20, CD163, CDC42, CTSK, CXCL11, CXCL13, CYP2C19, CYP2C9, ETS1, H19, HLA-F, HOTAIR, IL4R, LDHA, MERTK, MIR146A, NOTCH3, PADI4, PDPN, RAC1, RELA, S100A4, S100A9, SAA1, SEMA4D, SHH, TLR2, TLR9, XIST, YY1, and ZFAS1) connected by 206 edges. The gene discussed is SAA1; the disease is rheumatoid arthritis.