We are thinking that the difference of SHP‐1 status in between mutated KIT‐harboring (mastocytosis) and mutated RET‐harboring (MTC) cells would result in the different level of the formation of the CEACAM1‐SHP‐1 complex, and the followed different ratio of the CEACAM1‐SFKs complex/ CEACAM1‐SHP‐1 complex. The gene discussed is CEACAM1; the disease is medullary thyroid gland carcinoma.