Examination of CD26/DPPIV, p53, and PTEN expression in thyroid follicular adenoma.

Tumor cytology has proven to be inadequate for precise diagnosis of thyroid follicular adenoma. This suggests the need for a molecular approach for its diagnosis. Expression of CD26/DPPIV (dipeptidyl peptidas IV), p53, and PTEN was analyzed in smears or sections obtained from 19 patients with histologically proven thyroid follicular adenoma. Papanicolaou staining, CD26/DPPIV activity staining, and HE staining were performed and the specimens were observed morphologically. Immunohistochemical analysis using antibodies against p53 and PTEN was performed. Genetic mutation of PTEN exons was performed using the laser capture microdissection method. The nuclear area of the CD26/DPPIV-positive cells was significantly larger than that of the CD26/DPPIV-negative cells. p53 expression was not observed any specimen. PTEN expression was observed in 18 of 19 cases. DNA sequence analysis did not reveal mutations in exons 5-9 of PTEN in the immunohistochemically PTEN-negative case. In accordance with our previous reports, we found that observation of concomitant CD26-positive and PTEN-negative status in cases of follicular adenoma suggests a state close to follicular carcinoma or progression to cancer, thus warranting careful follow-up.