Advancing Novel Therapeutic Approaches to Treat Rare Forms of Sarcoma
Key Findings
- Massachusetts General Hospital was one of 27 international sites participating in a phase II clinical trial of a novel immunotherapy targeting rare forms of soft-tissue sarcoma
- Afami-cel is the first FDA-approved therapy specifically for metastatic synovial sarcoma and the first-ever FDA-approved TCR therapy for any sarcomas
- Afami-cel is an effective treatment for patients with metastatic or unresectable synovial sarcoma who received previous chemotherapy
Physician-scientists at Massachusetts General Hospital recently participated in a phase II clinical trial evaluating the use of adoptive T cell receptor (TCR) therapy to target patients with synovial sarcoma.
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Patient responses to afamitresgene autoleucel (afami-cel) during the SPEARHEAD-1 clinical trial resulted in its accelerated Food and Drug Administration (FDA) approval. This pathway enables the FDA to approve therapies for life-threatening diseases or conditions for which an unmet medical need exists.
"Because synovial sarcoma is almost universally fatal when metastasis develops, there has long been a need to identify better treatment options," says Edwin Choy, MD, PhD, director of the Center for Sarcoma and Connective Tissue Oncology at Mass General. "This is particularly exciting not only in the patient's response to the therapy but also the demonstrated effectiveness of a vastly different treatment paradigm for these rare cancers."
Afami-cel is the first FDA-approved therapy specifically for metastatic synovial sarcoma (SS) and the first-ever FDA-approved TCR therapy for any sarcomas.
Expanding Treatment Options for a Rare Disease
Soft-tissue sarcomas are tumors that tend to form in connective tissue surrounding bones and joints. Although extremely rare, approximately 1% of adult cancers in the U.S., there are more than 70 subtypes that present varying levels of metastatic aggressiveness. A complicating factor in the diagnosis and timely treatment of these tumors is that they frequently present as a bump on a leg or arm that can just as easily be mistaken for an injury or bug bite rather than a cancerous mass.
SS and myxoid round cell liposarcoma (MRCLS) are two of the more aggressive subtypes of soft-tissue sarcoma. Although both may be initially responsive to local (radiation or surgical resection) or systemic (chemotherapy) treatment, their high metastatic potential complicates efforts to achieve sustainable, long-term responses to available treatments.
As a result, five-year survival rates remain below 15% for those with advanced metastatic SS or MRCLS, with overall response rates (ORRs) to subsequent rounds of treatment after first-line therapy as low as 20%.
Many cancer cells in SS and MRCLS tumors display elevated levels of a protein called melanoma-associated antigen A4 (MAGE-A4), the expression of which is comparatively low or entirely absent in most normal cells. When MAGE-A4 is processed within these cells, a protein fragment is presented on the cell surface bound to a human leukocyte antigen (HLA). Recognition of this HLA/MAGE-A4 complex by T cells can potentially trigger an immune response resulting in the destruction of the cell.
Dr. Choy explains that this combination of unique, non-mutated, tumor-associated targets distinguishes them as singularly valuable in a therapeutic setting. "Exclusive overexpression of MAGE-A4 in tumors and their presentation by an HLA unique to patients offers a degree of specificity rare in cancer treatment."
Increasing the Accuracy and Effectiveness of Targeted Cancer Therapy
To capitalize on this, afami-cel therapy involves the collection of a patient's T cells and alteration of the T cell receptors to increase their affinity for the HLA/MAGE-A4 complex. Expansion of the resulting engineered T cell population occurs over the course of six weeks prior to a single intravenous infusion of the cells back into the patient.
Although similar to chimeric antigen receptor (CAR) T-cell therapy, afami-cel therapy presents important distinctions. In CAR T-cell therapy, T cells from a patient are engineered to produce a synthetic receptor that recognizes an abnormal protein found on the surface of some cancer cells. However, CARs require the target protein to be naturally occurring at the cell surface.
By contrast, afami-cel therapy can target proteins that are not naturally expressed on the cell surface, as intracellular proteins can be processed and have parts of the protein presented to the cell surface when processed with HLA proteins selectively targeting the HLA/MAGE-A4 complex on those cells.
Dr. Choy emphasizes that this level of selectivity requires careful screening to establish patient eligibility. This is because not all SS or MRCLS tumor cells demonstrate sufficient MAGE-A4 expression or not all patients have the specific HLA type (HLA*02) required for this therapy.
"The clinical trials for this therapy targeted patients experiencing metastasis or refractory disease after having undergone at least one—and often multiple—rounds of treatment using standard therapies," Dr. Choy explains. In this context, afami-cel therapy offers another therapeutic option at a point in treatment when response rates tend to decrease.
Promising Outcomes and Future Challenges
The SPEARHEAD-1 phase II trial looked at 52 patients—44 SS and 8 with MRCLS—who received afami-cell therapy and were followed for a median of 32.6 months. Major outcomes reported in The Lancet included:
- An ORR of 37% (38.6% for SS and 25% for MRCLS)
- A median overall survival (OS) time of 15.4 months for the overall population and an OS probability of 60% at 12 months post-treatment
Although all patients displayed varying degrees of side effects related to the treatment, Dr. Choy advises that they were relatively manageable when compared to commonly encountered side effects associated with standard treatments.
At the time of publication (3 years and 8 months after trial initiation), the authors also noted that 11 (21%) patients were still alive and undergoing follow-up observation. Dr. Choy suggests that the significance of these outcomes includes both a reported efficacy similar to first-line therapies and the extended OS and duration of response in some patients.
"The positive impact of this therapy is very promising," he advises. "The long-term benefits achieved by a subset of patients is particularly exciting and warrants additional research to identify the mechanisms driving those outcomes."
Capitalizing on an Infrastructure Built for Discovery
Among the benefits of research and clinical practice at Mass General, Dr. Choy highlights the streamlined infrastructure in place to support participation in clinical trials. "The resources are available and fine-tuned to help navigate coordinating and conducting a clinical trial," he says.
In the case of rare diseases, he emphasizes the difficulties inherent in simply making progress. "Most oncologists don't even know what synovial sarcoma is," Dr. Choy advises. "Participating in work of this caliber requires institutional support and infrastructure present at a place like Mass General, which encourages interactions with major cancer centers across the world."
Ultimately, collaborations within the Mass General ecosystem are frequently the difference between something being possible or impossible. "We're incredibly fortunate to have an exceptional Cellular Immunotherapy Program," says Dr. Choy. "Without their expertise, patients here would not have had access to this groundbreaking therapy."