OBJECTIVE:

To determine whether changes in expression level of the phosphatase and tensin homolog deleted on the chromosome 10 (PTEN) gene are associated with malignant transformation in mammary gland tumors in dogs.

SAMPLE POPULATION:

Specimens of 5 benign and 8 malignant mammary gland tumors and 2 unaffected mammary glands from dogs.

PROCEDURE:

The open reading frame (ORF) sequence of PTEN gene in each specimen was analyzed via a direct-sequencing method; expression levels of PTEN gene were quantified via a competitive reverse transcription (RT)-PCR method.

RESULTS:

Compared with findings in clinically normal samples, amounts of PTEN mRNA were increased 2- to 4-fold in 4 of the 5 benign mammary gland tumor samples. In contrast, PTEN expression was remarkably low in 4 of the 8 malignant tumor samples (approx 12% to 37% of the level in unaffected mammary gland specimens). Gene amplification via the RT-PCR method with total RNA prepared from malignant tumor samples as a template yielded 3 bands that were smaller than the full-length ORF product of PTEN gene; in 2 of those 3 RT-PCR products, exons 6 and 7 or exons 3 to 8 were absent. No mutation was detected in the full-length ORF product of PTEN gene.

CONCLUSIONS AND CLINICAL RELEVANCE:

Results suggested that a decreased level of PTEN gene expression (compared with unaffected mammary gland tissue) is associated with malignancy in canine mammary tumors. Analysis of PTENgene expression level in dogs with mammary gland tumors may provide useful prognostic information.