A 4 bp deletion was found in the‏ intron 2 of the Hspb1 gene in the three cat mammary‏ tumors (CP7, CP16, CP28), which is homozygous in‏ two (CP7, CP28), and heterozygous in one neoplastic‏ tissue, as well as the blood of one animal (CP16,‏ CP16b) samples. The gene discussed is PRB2; the disease is breast cancer.