CRLF2 and acute lymphoblastic leukemia: In cases of BCP-ALL, HHD reportedly occurs in 25-30% [9,15], P2RY8::CRLF2 in 6%, high CRLF2 expression in 4.7%, and concurrent P2RY8::CRLF2 and high CRLF2 expression in 2-3% [8].