Canadian Multicenter Project on Standardization of Programmed Death-Ligand 1 Immunohistochemistry 22C3 Laboratory-Developed Tests for Pembrolizumab Therapy in NSCLC.

INTRODUCTION: The programmed death-ligand 1 (PD-L1) immunohistochemistry (IHC) assay is used to select patients for first or second-line pembrolizumab monotherapy in NSCLC. The PD-L1 IHC 22C3 pharmDx assay requires an Autostainer Link 48 instrument. Laboratories without this stainer have the option to develop a highly accurate 22C3 IHC laboratory-developed test (LDT) on other instruments. The Canadian 22C3 IHC LDT validation project was initiated to harmonize the quality of PD-L1 22C3 IHC LDT protocols across 20 Canadian pathology laboratories. METHODS: Centrally optimized 22C3 LDT protocols were distributed to participating laboratories. The LDT results were assessed against results using reference PD-L1 IHC 22C3 pharmDx. Analytical sensitivity and specificity were assessed using cell lines with varying PD-L1 expression levels (phase 1) and IHC critical assay performance controls (phase 2B). Diagnostic sensitivity and specificity were assessed using whole sections of 50 NSCLC cases (phase 2A) and tissue microarrays with an additional 50 NSCLC cases (phase 2C). RESULTS: In phase 1, 80% of participants reached acceptance criteria for analytical performance in the first attempt with disseminated protocols. However, in phase 2A, only 40% of participants reached the desired diagnostic accuracy for both 1% and 50% tumor proportion score cutoff. In phase 2B, further protocol modifications were conducted, which increased the number of successful laboratories to 75% in phase 2C. CONCLUSIONS: It is possible to harmonize highly accurate 22C3 LDTs for both 1% and 50% tumor proportion score in NSCLC across many laboratories with different platforms. However, despite a centralized approach, diagnostic validation of predictive IHC LDTs can be challenging and not always successful.

Hybrid chromophobe renal cell neoplasm.

Hybrid renal cell neoplasms (HRCNs) containing areas of tumor cells displaying cytological features of chromophobe renal cell carcinoma (CHRCC) and renal oncocytoma (RO) have been recently described in patients with renal oncocytosis and Birt-Hogg-Dube (BHD) syndrome (autosomal dominant genodermatosis). In this study, we identified cases of sporadic HRCN. We reviewed 425 consecutive renal cell carcinomas (RCC), 18 CHRCC, six HRCN, and 25 RO. Five HRCN were identified, including four from the group of RCC and two from RO. Patient age ranged from 40 to 68 years (mean age: 54 years), and the male:female ratio was 4:1. Tumors measured from 1.8 to 5 cm (mean diameter: 3.0 cm). Tumoral necrosis was not seen. Vascular invasion into medium-sized veins was identified in one HRCN. Chromophobe cells accounted for 20-80% of the tumors. Hale's colloidal stain showed weak to moderate diffuse cytoplasmic staining in scattered cells corresponding to those displaying routine staining features of chromophobe cells. Areas of oncocytic cells in studied tumors and control oncocytomas showed negative or focal cytoplasmic staining usually bordering extra- or intra-cytoplasmic lumina. Immunostaining for cytokeratin 7 and vimentin showed focal immunoreactivity in three cases and negative reactivity in all six cases, respectively. None of the study cases had microscopic RO, as commonly seen in renal oncocytosis, or were associated with BHD syndrome Sporadic HRCN accounted for 1% of RCC. They were of smaller size than RCC and were associated with a favorable prognosis.