PIK3CA and PTEN mutations in uterine endometrioid carcinoma and complex atypical hyperplasia

The tumor suppressor PTEN gene and the PIK3CA oncogene are frequently mutated in uterine endometrioid carcinoma (UEC). PTEN mutations are also common in complex atypical hyperplasia (CAH), the precursor lesion of UEC. The status of PIK3CA has not yet been explored in CAH. In this study, we evaluated both CAH and UEC for PTEN and PIK3CA mutations.

Neoplastic tissue was microdissected, and DNA was extracted from 29 cases of CAH. DNA was available from 44 UEC cases previously characterized for PTEN mutations. Direct DNA sequencing of exons 9 and 20 of the PIK3CA gene was done on all 73 cases. In addition, CAH cases were analyzed for PTEN mutations. Statistical analyses were done using the Fisher's exact test.

Two (7%) of 29 CAH and 17 (39%) of 44 UEC cases contained a PIK3CA mutation (P = 0.003). Fourteen (48%) of 29 CAH cases had a PTEN mutation, but none contained both a PTEN and PIK3CA mutation. Twenty-five (57%) of 44 UEC cases had a PTEN mutation, and 12 (48%) of these 25 cases also contained a PIK3CA mutation. Coexistent PIK3CA and PTEN mutations were significantly correlated with UEC compared with CAH (P = 0.002), but the association in UEC did not reach statistical significance (P = 0.21).

PIK3CA is the most commonly mutated oncogene in UEC; however, mutations are uncommon in CAH. Thus, mutations in PIK3CA, unlike PTEN mutations, are associated with invasion. These findings suggest that mutations in PIK3CA may serve as a marker of invasion with potential clinical use. Furthermore, PIK3CA and PTEN mutations may play distinct roles in endometrial tumorigenesis.