The TetRS qPCR-based rapid genotyping panel detects recurrent molecular alterations relevant to the diverse radiologic differential diagnosis of PCNSL and subsequent diagnostic workup. (A) Clinical characteristics of 159 patients who established a new diagnosis of PCNSL at our facility. Diagnostic assays include all procedures performed at our facility and outside facilities. Time to diagnosis is displayed on a logarithmic scale, calculated from date of admission to our facility. One patient is not displayed, who had 4 lumbar punctures as an outpatient, with the final assay returning positive on the first day of inpatient admission. This cohort included 2 HIV-positive (1.3%), 17 EBV-positive (10.7%), and 13 immunosuppressed patients (8.2%) (supplemental Table 1). (B) Final diagnosis among patients with a new brain lesion with PCNSL in the differential diagnosis. (C) A representative patient with a new brain lesion underwent 2 nondiagnostic lumbar punctures prior to a brain biopsy. Intraoperative histopathology was inconclusive. Chemotherapy was initiated empirically prior to final pathologic diagnosis due to symptomatic decline. Analysis of archived biopsy tissue revealed the MYD88 L265P mutation. (D) Results of TetRS assay on DNA extracts from 71 archived, clinically annotated biopsy specimens by sensitive detection of hotspot mutations in MYD88, TERT promoter, IDH1/2, H3F3A, and BRAF. Expanded results are shown in supplemental Figure 7. EBV, Epstein-Barr virus; Hem., hematologic; HIV, human immunodeficiency virus.