Can thyroid histomorphology identify patients with PTEN hamartoma tumour syndrome?

Aims The phosphatase and tensin homologue (PTEN) hamartoma tumour syndrome (PHTS) is a genetic disorder with variable clinical presentation and increased lifetime risk of multiorgan malignancies. The thyroid gland is commonly affected with follicular nodular disease (FND) and follicular cell‐derived carcinomas. Histopathological and immunohistochemical assessment of thyroid disease in PHTS is essential to identify patients at‐risk. Methods and results In all, 30 PHTS patients with available thyroidectomy specimen material (2000–2023) and 31 control patients with FND and “adenomatous nodules” were retrieved. Histologic criteria, including the frequency of adenomatous‐type nodules versus hyperplastic‐type nodules, background and nodular lipomatous metaplasia, chronic lymphocytic thyroiditis, cytoplasmic clearing of follicular cells in nodules, nodule‐in‐nodule appearance, and spectrum of nuclear atypia between nodules were evaluated in both cohorts and a Thyroid Histomorphologic PHTS Score (THiPS) system was established with a cutoff of 4 points or higher being considered concerning for PHTS. In all, 27 PHTS (90%) and five control (16.1%) cases had THiPS ≥4. A PTEN immunohistochemical stain was evaluated in 25 cases of each cohort and showed nuclear and cytoplasmic loss of expression in all or most of the nodules of 24/25 PHTS cases. In 3/25 control cases, two with THiPS ≥4, had loss of expression in one to multiple nodules. Conventional papillary thyroid carcinomas in PHTS patients retained PTEN cytoplasmic expression. Conclusions Our study supports that, although not specific, the finding of multiple histologic features is found more frequently in patients with PHTS compared to the non‐PHTS control group. The THiPS system has high sensitivity for thyroid specimens from patients with PHTS. Multiple histologic features of thyroid follicular nodular disease are found frequently in patients with PTEN Hamartoma Tumour Syndrome. In this study we propose an exploratory Thyroid Histomorphologic PHTS Score system.