BACKGROUND/AIMS In 1998 the PPP2R1B gene encoding the A subunit of the serine/threonine protein phosphatase was identified as a putative tumour suppressor gene in lung and colon cancer in the chromosome region 11q22–24. The aim of the present study was to determine the type of alterations in primary rectal cancers as well as colon cancers and the correlation between these alterations and clinicopathological data.

RESULTS Five missense mutations producing amino acid substitutions were detected in the four colon cancer cases (13.3%; four of 30 colorectal cancers): ¹⁵glycine (GGT) to alanine (GCT) and ⁴⁹⁹leucine (TTA) to isoleucine (ATA) in the same case, and ⁴⁹⁸valine (GTG) to glutamic acid (GAG),⁵⁰⁰valine (GTA) to glycine (GGA), and ³⁶⁵serine (TCT) to proline (CCT). Of these five mutations, three (60%) were located in HEAT repeat 13 and four (80%) showed T to other nucleotide substitutions. In addition, a normal polymorphism,⁴⁷⁸leucine, was found. No correlation was found between these mutations and clinicopathological data.

CONCLUSION Our results suggest that the PPP2R1B gene is one of the true targets at 11q23, and its inactivation is involved in the development of all types of colorectal cancers.