EXHIBIT 99.1

SELLAS Life Sciences Provides Business Update and Reports First Quarter 2019 Financial Results

Company to Present Data at Upcoming American Society of Clinical Oncology (ASCO) Annual Meeting

NEW YORK, May 15, 2019 -- SELLAS Life Sciences Group, Inc. (Nasdaq: SLS) (“SELLAS” or the “Company”), a clinical-stage biopharmaceutical company focused on the development of novel cancer immunotherapies for a broad range of cancer indications, today provided a business update and reported financial results for the quarter ended March 31, 2019.

“Throughout 2019, as we have been progressing the review of strategic alternatives, we also have been continuing to advance our novel cancer immunotherapy clinical pipeline and are excited to be presenting data on one of our clinical candidates, nelipepimut-S (NPS), at the upcoming American Society of Clinical Oncology (ASCO) Annual Meeting,” said Angelos Stergiou, MD, ScD h.c., President and Chief Executive Officer of SELLAS.

American Society of Clinical Oncology 2019 Annual Meeting

Sellas will present immunologic response data from the NPS/Trastuzumab Study will be presented at the upcoming ASCO Annual Meeting being held May 31 - June 4, 2019 in Chicago, IL. Details for the presentation are as follows:
Title: Immunologic responses in triple-negative breast cancer patients in a randomized phase IIb trial of nelipepimut-S plus trastuzumab versus trastuzumab alone to prevent recurrence
Presenter: Jessica Campf, MD, San Antonio Military Medical Center
Abstract Number: 556
Poster Session: “Breast Cancer - Local/Regional/Adjuvant”
Date and Time: June 2, 2019, 8:00 am - 11:00 am CDT
Location: Hall A, McCormack Place, Chicago, IL

First Quarter 2019 and Recent Highlights

Galinpeptimut-S (GPS)
In February 2019, the Company announced that Richard Maziarz, M.D., Medical Director of the Adult Blood and Marrow Stem Cell Transplant & Cellular Therapy Program at the Knight Cancer Institute and Professor of Medicine at Oregon Health and Science University (OHSU), and Roisin O'Cearbhaill, M.D., Assistant Attending Physician in Gynecologic Medical Oncology Service at Memorial Sloan Kettering Cancer Center (MSKCC), will serve as co-principal investigators of the Company’s Phase 1/2 open-label, non-comparative, multicenter, multi-arm study of GPS in combination with Merck’s anti-PD-1 therapy KEYTRUDA® (pembrolizumab) in patients with selected WT1-positive advanced cancers, including both hematologic malignancies and solid tumors. The study is assessing the efficacy and safety of the combination, with exploratory long-term follow-up for overall survival and safety. 
In April 2019, the Company announced an agreement with MSKCC to conduct an investigator-sponsored clinical trial of GPS in combination with Bristol-Myers Squibb’s anti-PD-1 therapy, nivolumab, in patients with malignant pleural mesothelioma (MPM). The Phase 1 open-label clinical study will enroll patients with MPM who harbor relapsed or refractory disease after having received frontline standard of care multimodality therapy with study drug provided by both SELLAS and Bristol-Myers Squibb.
Nelipepimut-S (NPS)
In February 2019, the Company announced preliminary immune response data from an analysis of the patterns of induction of NPS-specific T-cell responses over time in a subgroup of patients with triple-negative breast cancer (TNBC) from the prospective, randomized, single-blinded, controlled Phase 2b independent investigator-sponsored clinical study of the combination of trastuzumab (Herceptin®) +/- NPS targeting HER2 low-expressing breast cancer patient cohorts (the NPS/Trastuzumab Study). CD8+ cytotoxic T-lymphocytes (CTLs) from peripheral blood samples from study patients with TNBC were measured using specifically designed NPS-specific dextramers in a flow cytometry-based assay in duplicate. In 64 evaluable TNBC patients (39 in the NPS plus trastuzumab arm; 25 in the trastuzumab alone arm) across a median of four time-points (including baseline), NPS + trastuzumab administration generated up to 3-fold higher frequencies of NPS-specific CTLs compared to trastuzumab alone. CTL frequencies were higher among non-recurrent patients compared with those who recurred, on either arm.



The following information was filed by Sellas Life Sciences Group, Inc. (SLS) on Wednesday, May 15, 2019 as an 8K 2.02 statement, which is an earnings press release pertaining to results of operations and financial condition. It may be helpful to assess the quality of management by comparing the information in the press release to the information in the accompanying 10-Q Quarterly Report statement of earnings and operation as management may choose to highlight particular information in the press release.

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