LEF1 stained positive in all 5 Sertoli cell tumors and zero of 12 Leydig cell tumors — promising signal, absurdly small dataset
Journal: Annals of Diagnostic Pathology | Published: 2026-02-03 | Type: Retrospective case series | PMID: 41671911 Authors: Della Mura M et al., four Italian institutions (Bari, Catanzaro, Barletta-Andria-Trani, Lecce) Funding/COI: Not listed; authors declare no conflicts of interest
Testicular sex cord-stromal tumors are rare — Leydig cell tumors (LCTs) and Sertoli cell tumors (SCTs) being the main subtypes — and telling them apart under the microscope can be genuinely difficult. This small retrospective study from four Italian pathology departments tested LEF1, a transcription factor downstream of the Wnt/β-catenin pathway, as a diagnostic immunohistochemical marker. The headline result is clean: LEF1 was strongly positive in all five SCTs and negative in all twelve LCTs, controls, and non-neoplastic tissue. A secondary finding — focal IL13Rα2 expression in four of twelve LCTs — is novel but unexplained.
Seventeen cases is not a cohort — it is a case series. The 100% sensitivity and 100% specificity figures for LEF1 are derived from five SCTs and twelve LCTs diagnosed at four centers between 2020 and 2025, reviewed against current WHO and GUPS/ISUP TESST criteria. With n=5 in the SCT arm, confidence intervals around the sensitivity estimate span roughly 48% to 100%; the point estimate is essentially uninformative. Retrospective design, no blinding of pathologists to tumor type during staining interpretation, and no external validation cohort are the structural problems.
The immunohistochemistry methodology appears standard and multi-center review adds some robustness, but the fundamental limitation is case rarity — these tumors are uncommon enough that 17 cases over five years across four institutions is not surprising, and not a study design choice the authors can be faulted for. The paper appropriately calls for validation in larger cohorts.
This paper does one narrow thing adequately: it shows LEF1 stains SCTs and not LCTs in a tiny Italian series, which is consistent with what we'd expect from Wnt pathway biology. If you are a surgical pathologist occasionally encountering these rare tumors, the finding is worth noting as a supplementary marker when β-catenin staining is ambiguous. For anyone else, this is a preliminary signal that requires a five- to tenfold larger validation study before it can be called a diagnostic tool. The IL13Rα2 finding in LCTs is genuinely novel but currently meaningless — a footnote waiting for a study that can actually interrogate it.