Abstract P2-14-02: Overall survival following treatment with a modified whole tumor cell targeted immunotherapy in patients with advanced breast cancer
Authors: Williams William , Dakhil Shaker R , Calfa Carmen , Holmes Jarrod P , Bhattacharya Saveri , Lukas Jason , Tan-Chui Elizabeth , Peoples George E , Sunkari Vivek G , Lacher Markus D , Wiseman Charles L 
Published: March 2022

Background: SV-BR-1-GM is a GM-CSF secreting breast cancer cell line derived from a Grade II (moderately differentiated) breast tumor that also expresses HLA class I & II antigens and is able to function as an antigen-presenting cell. Irradiated SV-BR-1-GM is used in a regimen including pre-dose low-dose cyclophosphamide and post-dose injection of IFNα2b into the inoculation sites. The SV-BR-1-GM regimen has been used alone (“monotherapy”, ClinicalTrials.gov NCT03066947 - study completed) and in combination with checkpoint inhibitors (“combination”, ClinicalTrials.gov NCT03328026 - study ongoing). Here we report survival data for patients with advanced metastatic breast cancer (aMBC) treated with the SV-BR-1-GM regimen. Methods: 27 patients with refractory aMBC were treated with the SV-BR-1-GM regimen as monotherapy (cycles every 2 weeks x3 and then monthly). The combination study uses the SV-BR-1-GM regimen with PD-1 inhibitors (PD-1i) pembrolizumab or retifanlimab with cycles every 3 weeks (12 patients dosed to date). Here we report progression free survival (PFS) and overall survival (OS) for patients where that data was collected. Results: A total of 35 patients received the SV-BR-1-GM regimen. The SV-BR-1-GM regimen alone (monotherapy) was given to 27 and 12 received the regimen with a PD-1i checkpoint inhibitor (combination therapy): 4 subjects crossed over from monotherapy. Patients had been heavily pre-treated, median prior regimens = 5. Most patients were estrogen receptor and/or progesterone receptor positive, 18% were Her2/neu positive and 33% were triple negative. The treatment was generally safe and well tolerated. The disease control rate was 30% for the SV-BR-1-GM regimen alone and 33% for the combination with a PD-1i. Several patients had objective complete regression of selected metastases. Median progression free survival was 2.8 months for the SV-BR-1-GM regimen alone and 4.2 months for the PD-1i combination. Median overall survival was 7.0 months for the SV-BR-1-GM regimen alone (data available on 9 patients), and 12.0 months for the PD-1i combination (data available on 7 patients). Conclusions: The median OS compares favorably with published data regarding survival in third line trials (Kazmi Breast Cancer Res Treat. 2020 Aug 17). The protracted OS seen in some subjects suggests some patient subpopulations are more likely to derive clinical benefit. The SV-BR-1-GM regimen alone or in combination with a PD-1i, when administered to heavily pre-treated patients with aMBC, may have elicited effective immune responses in some patients.

TablePatients by StudyCharacteristicSV-BR-1-GM Regimen Alone (n=27)SV-BR-1-GM Regimen + PD-1i (n=12)All Patients* (n=35)Age60 ± 1063 ± 1060 ± 10Mean Prior Systemic Regimens5 (range 0-12)6 (range 1-10)5 (range 0-12)% ER/PR +52%75%58%% Her2/neu +15%17%18%% Triple Negative36%25%33%Delayed-type Hypersensitivity81%91%82%Disease Control Rate30%33%29%Median (Range) Progression Free Survival (months)2.8 (0.4-7.4) (n=27)4.2 (0.8-9.4) (n=11)2.8 (0.4-9.4) (n=34)Median (Range) Overall Survival (months)7.0 (1-41) (n=9)12.0 (5.1-21.4) (n=7)10.2 (1-41) (n=14)• Note that 4 patients crossed over from the monotherapy study to the combination therapy study.

Citation Format: William Williams, Shaker R Dakhil, Carmen Calfa, Jarrod P Holmes, Saveri Bhattacharya, Jason Lukas, Elizabeth Tan-Chui, George E Peoples, Vivek G Sunkari, Markus D Lacher, Charles L Wiseman. Overall survival following treatment with a modified whole tumor cell targeted immunotherapy in patients with advanced breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-14-02.