MorningSun Data Show Sub-Q Mosunetuzumab Improves QOL for Oldest Patients With DLBCL

For decades, the cancer regimen known as R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine [Oncovin], prednisone) has been the standard first-line treatment for diffuse large B-cell lymphoma (DLBCL), curing at least 60% of patients who receive it.

But that leaves a sizable number of patients with DLBCL who relapse or can’t start R-CHOP because they can’t tolerate it. The annual meeting of the American Society of Clinical Oncology (ASCO) offered new options for many of these patients.

Among them, Ian W. Flinn, MD, PhD, chief scientific officer for OneOncology, presented data June 1, 2026, from the DLBCL cohort of the MorningSun study (NCT05207670), which is a phase 2 basket study that evaluated subcutaneous mosunetuzumab in patients with B-cell non-Hodgkin lymphoma. Specifically, results showed this fixed-duration regimen offers an effective treatment and good quality of life for patients with DLBCL who are at least 80 years old or those 65 to 79 years of age who are ineligible for chemoimmunotherapy.¹

Right now, mosunetuzumab (Lunsumio; Genentech) is approved for adult patients with relapsed or refractory follicular lymphoma who have already received at least 2 prior lines of therapy.

Why the Hard Cutoff at Age 80 for R-CHOP?

Many treatment guidelines and clinical trials use age 80 as a key threshold, as studies in geriatric oncology find that patients at this age or older have compressed physiologic reserve, are more likely to be taking multiple medications for other conditions, and have higher sensitivity to treatment-related toxicity.^2,3 Because these patients have unmet needs, MorningSun explicitly targeted this population to generate prospective data that are currently lacking.¹

Mosunetuzumab is a CD20xCD3 T-cell–engaging bispecific antibody that redirects endogenous T cells to eliminate malignant B cells, bypassing the need for cytotoxic chemotherapy entirely. This mechanism is particularly appealing in elderly and unfit patients, where the toxicity burden of combination regimens—myelosuppression, neuropathy, cardiotoxicity—can be prohibitive and potentially life-threatening.^1-3

Unlike some combination approaches being explored at ASCO 2026, single-agent mosunetuzumab carries a fundamentally different toxicity profile, one potentially better matched to patients with reduced physiologic reserve.

The MorningSun Regimen: Outpatient Treatment

The MorningSun regimen for this cohort called for patients to be treated in an outpatient setting, and to receive the therapy on the following schedule: 5 mg on day 1, 45 mg on day 8, and 45 mg on day 15 for cycle 1; then, 45 mg on day 1 for up to 17 cycles of 21 days each. Thus, besides its reduced toxicity, the MorningSun regimen offers older patients the option of a clear time frame.

The primary end point was progression-free survival (PFS) rate at 24 months. Other end points included overall survival (OS); objective response rate (ORR); complete response (CR) rate; change from baseline (CfB) in lymphoma symptoms as assessed by the Functional Assessment of Cancer Therapy-Lymphoma subscale (FACT-Lym), with higher scores indicating improvement (a ≥ 3-point increase is considered clinically meaningful); and safety.¹

The MorningSun cohort enrolled 49 patients with a median age of 83 years, with an age range extending to 101 years. Over half carried high-risk International Prognostic Index scores of 3 to 5, and nearly 1 in 5 patients had bulky disease. Enrollment was predominantly community-based, reflecting the real-world settings where most patients are seen.

Data Show Outpatient Administration Safe and Appropriate

Flinn, who is also chief scientific officer for Tennessee Oncology updated data from the abstract released May 21, 2026. The updated data, reflecting a median follow-up of 23.3 months, show the 12-month PFS rate was 66.3% (95% CI, 49.9-78.0) with median PFS not reached. The ORR was 73.5% and the CR was 59.2%. The 24-month PFS rate was 56.4% (95% CI, 39.4-70.3).

OS at 12 months was 73% (95% CI, 58.4-84.2) and 67.3% at 24 months (95% CI, 50.5-79.5).

Of note, the safety profile supported outpatient administration. The most common adverse event was injection site reaction, occurring in 53% of patients but universally grade 1 or 2. Cytokine release syndrome occurred in 12.2% of patients, all grade 1 or 2, and all resolved.¹

Infection rates, while notable at 53.1%, were nearly all grade 1 and were resolved in 92.3% of cases. Four patients died due to adverse events but these deaths were not attributed to mosunetuzumab by investigators, who noted the absence of chemotherapy-related toxicities such as febrile neutropenia or significant neuropathy.

Patient-reported outcomes demonstrated clinically meaningful improvements in lymphoma symptoms in 57.1% of patients, with FACT-Lym subscale scores rising steadily through treatment. In a population for whom quality of life is often the primary treatment goal, the study authors suggested that this point was noteworthy.

Subcutaneous mosunetuzumab, “showed promising efficacy with manageable safety in elderly/unfit patients with previously untreated DLBCL in an outpatient setting,” they wrote. “Clinically meaningful improvements in lymphoma symptoms suggest that [this therapy] improves aspects of health-related quality of life in this population.”

Note: This article was updated to include new data presented at ASCO.

References

1. Flinn IW. Burke JM, Tun AM, et al. Fixed-duration subcutaneous (SC) mosunetuzumab (Mosun) in elderly/unfit patients with previously untreated diffuse large B-cell lymphoma (DLBCL): Interim analysis and patient-reported outcomes (PROs) from the phase 2 MorningSun study. J Clin Oncol. 2026;44(suppl 16):abstr 7029. doi:10.1200/JCO.2026.44.16_suppl.7029
2. Toby A. Eyre, William Wilson, Amy A. Kirkwood, et al. Infection-related morbidity and mortality among older patients with DLBCL treated with full- or attenuated-dose R-CHOP. Blood Adv 2021; 5 (8): 2229–2236 doi: https://doi.org/10.1182/bloodadvances.2021004286
3. Coiffier B, Sarkozy C. Diffuse large B-cell lymphoma: R-CHOP failure-what to do? Hematology Am Soc Hematol Educ Program. 2016 Dec 2;2016(1):366-378. doi: 10.1182/asheducation-2016.1.366