Comparison of immunohistochemistry and next-generation sequencing results in oncogenic PTEN missense mutations

Background: Phosphatase and tensin homolog (PTEN) is one of the most frequently mutated tumor suppressor genes in malignant tumors. Oncogenic PTEN mutations have diagnostic, prognostic, and therapeutic implications. Similar to TP53 mutations, oncogenic PTEN mutations can result from nonsynonymous missense mutations. However, there has been no detailed study on the immunostaining pattern of oncogenic PTEN missense mutations. Methods: We retrospectively selected 18 cancers (13 endometrial cancers, 2 brain tumors, 1 ovarian cancer, 1 lung cancer, and 1 cancer of unknown origin) harboring oncogenic PTEN missense mutations, which were confirmed by targeted next-generation sequencing. PTEN immunohistochemistry was conducted for all cases, and the results were compared with sequencing results. Results: The immunostaining results of PTEN missense mutations revealed a diverse pattern depending on the site of mutation and co-occurring mutation. The most frequent oncogenic PTEN mutations were R130G (4/18, 22.2 %) and R130Q (3/18, 16.7 %). Eleven cases harbored PTEN missense mutations only, whereas the remaining seven cases harbored PTEN truncating mutations and PTEN missense mutations. Complete loss of cytoplasmic expression were found in five cases, of which three had missense mutation only. PTEN R130 residue mutation alone did not showed altered PTEN immunostaining pattern in this study. Conclusions: PTEN missense mutation, which comprises a portion of oncogenic PTEN mutation, can manifest as a diverse immunostaining pattern. Complementary testing using both immunostaining and next-generation sequencing should be conducted to accurately evaluate the PTEN status in malignancy.