PTEN LDT

This laboratory developed test (LDT) aids in the assessment of PTEN protein status in tumor tissue. The assay may support identification of tumors demonstrating PTEN loss, which is associated with activation of the PI3K/AKT/mTOR pathway. PTEN protein expression is evaluated in formalin‑fixed, paraffin‑embedded tissue specimens using a rabbit monoclonal anti‑PTEN antibody (clone SP218). Expression is assessed based on cytoplasmic staining in tumor cells, with internal non‑neoplastic elements serving as staining controls when present. The test is performed in accordance with CAP and CLIA LDT requirements. 

At present, FDA guidelines recommend PTEN testing, by IHC, in prostatic adenocarcinoma. Although loss of PTEN expression has been observed in other carcinoma types, the predictive value of PTEN immunohistochemistry for guiding therapy decisions in these tumors has not been established, and no reliable scoring criteria exist. Accordingly, the use of PTEN expression status to predict response to any medication, including TRUQAP® (capivasertib), in tumors other than prostatic adenocarcinoma should be interpreted within the context of these limitations and should not serve as the sole basis for treatment decisions.

Scoring and interpretation: 
PTEN Loss Detected (Positive): ≥90% of viable tumor cells show absence of cytoplasmic staining  
PTEN Loss Not Detected (Negative): <90% of viable tumor cells show absence of cytoplasmic staining Results are reported qualitatively as PTEN Loss Detected or PTEN Loss Not Detected.