Background: Relapsed/refractory (r/r) DLBCL patients (pts) are characterized by poor prognosis. Copanlisib is a pan-Class I phosphatidylinositol 3-kinase (PI3K) inhibitor, with modest single-agent activity in unselected DLBCL pts. Here we report the treatment effect of copanlisib in r/r DLBCL pts with regards to cell of origin (COO) and molecular biomarker profiles (NCT02391116). Methods: Patients with r/r DLBCL and ≥1 prior lines of therapy were eligible. Copanlisib (60 mg IV infusion) was administered on days 1, 8 and 15 of a 28-day cycle. Tumor samples were evaluated for COO, CD79B mutations and > 400 genes by next generation sequencing (NGS). The primary endpoint was objective tumor response rate (ORR; per Lugano Classification, 2014) by COO and CD79B status. Results: The full-analysis (FAS) and per-protocol sets (PPS; ≥3 doses, post-baseline scans and NGS/COO data) included 67 and 40 pts, respectively. Pts were 58% male, median age 69 (range 25-93), ECOG status 0/1/2 22%/57%/21%, and heavily pretreated (median prior lines = 3, range 1-13). In the PPS, COO (and mutant CD79B status) analysis identified 22 GCB DLBCL (2 mutant), 16 ABC DLBCL (6 mutant), and 2 unclassifiable. The ORR in the PPS was 25% (10 of 40), with 5 complete responses (CR) and 5 partial responses (PR); stable disease in 12 pts. The ORR was 13.6% with 1 CR in GCB pts and 37.5% with 4 CRs (25%) in ABC pts. Response to copanlisib was 25% in pts with (2/8) and without (8/32) CD79B mutations. Five of 10 ABC DLBCL-wtCD79B pts and one GCB DLBCL-mCD79B responded (ongoing > 17 cycles). NGS analysis in 54 pts detected 348 mutations; BCL2 (54% of pts), TP53 (41%), BCL6 (30%), MYC (22%), CD79B (19%)/A (6%), MYD88 (19%), TNFAIP3 (17%), CARD11 (13%), and NFKBIA (9%). Response to copanlisib was not significantly different based on BCL2, BCL6, MYC, and MYD88 mutations. With a median of 6 cycles (range 1-29), the most common AEs (% all grade/gr3+4) were diarrhea (36/2), nausea (31/2), fatigue (31/3), fever (21/2) and transient hypertension (40/33) and hyperglycemia (34/31). There were 14 gr5 AEs (none drug-related). Conclusions: Copanlisib treatment of r/r DLBCL pts resulted in encouraging responses, especially in the ABC subtype, with a manageable toxicity. Clinical trial information: NCT02391116