FDA Grants Fast Track Designation to SOT106 for Soft Tissue Sarcoma

The FDA has granted fast track designation (FTD) to SOT106, an investigational antibody-drug conjugate (ADC) targeting leucine-rich repeat-containing 15 (LRRC15), for the treatment of soft tissue sarcoma (STS). SOTIO Biotech, the sponsor, plans to initiate a first-in-human clinical trial of SOT106 later this year.¹

This is the second FTD granted to a SOTIO ADC program in recent months; the company's other lead ADC, SOT109, which targets CDH17 for colorectal cancer, received FTD in July 2026.

SOT106 previously received FDA orphan drug designation for osteosarcoma in May 2026, ahead of the planned first-in-human trial. The new FTD for soft tissue sarcoma extends the regulatory support for SOT106 across additional high-need sarcoma indications.

LRRC15 is broadly expressed across multiple highly prevalent sarcoma subtypes and is described by the company as a clinically validated target, positioning SOT106 to potentially address a broad population of patients with STS who have limited therapeutic options.

“Soft tissue sarcomas remain a major unmet medical need, where decades of therapeutic progress have yet to translate into meaningful improvements for patients with advanced or recurrent disease,” Vivi Boura, MD, chief medical officer of SOTIO, stated in a news release. “Receiving [FTD] for SOT106 is an important regulatory milestone that reinforces this program's potential to improve outcomes for patients facing these difficult-to-treat cancers.”

Mechanism and Target Rationale

LRRC15 is a mesenchymal and stromal antigen associated with tumor invasion and with resistance to chemotherapy and immunotherapy, which supports its use as an ADC target beyond conventional tumor-cell antigens. SOT106 couples an anti-LRRC15 antibody to a cytotoxic payload and has shown antitumor activity in preclinical models of both osteosarcoma and soft tissue sarcoma, with a tolerability profile the company describes as supporting a high therapeutic index.^1,2 Another ADC targeting LRRC15, samrotamab vedotin (ABBV-085), was evaluated in a phase 1 trial in advanced sarcomas and other solid tumors and resulted in an overall response rate of 20% among patients with osteosarcoma and undifferentiated pleomorphic sarcoma treated at the expansion dose, with no responses observed in other tumor types.³

Regulatory and Development Context

FTD is intended to facilitate development and expedite review of therapies for serious conditions that address unmet medical needs. The designation provides for more frequent interactions with the FDA and may support an accelerated pathway through eligibility for rolling review and priority review if applicable criteria are met.

Beyond SOT106 and SOT109, SOTIO's pipeline includes SOT201, a next-generation PD-1–targeting immunocytokine currently being evaluated in the phase 1 VICTORIA-01 study (NCT06163391) in patients with solid tumors. The company has described both SOT106 and SOT109 as potential best-in-class ADCs designed to rapidly advance to clinical proof of concept.¹

Boura said the company's goal is to translate SOT106's design into a new option across sarcoma subtypes. “As we advance SOT106 toward the clinic, we aim to translate its differentiated design and LRRC15-targeting strategy into a novel therapeutic approach with the potential to offer a new treatment option for patients across multiple soft tissue sarcoma subtypes,” she stated in the news release.

REFERENCES

1. FDA Grants Fast Track Designation to SOTIO's SOT106 ADC for Soft Tissue Sarcoma Treatment, Accelerating Clinical Development. News release. SOTIO Biotech. August 26, 2026. Accessed August 26, 2026. https://tinyurl.com/47s9dv3m

2. Purcell JW, Tanlimco SG, Hickson J, et al. LRRC15 Is a novel mesenchymal protein and stromal target for antibody-drug conjugates. Cancer Res. 2018;78(14):4059-4072. doi:10.1158/0008-5472.CAN-18-0327

3. Demetri GD, Luke JJ, Hollebecque A, et al. First-in-human phase I study of ABBV-085, an antibody-drug conjugate targeting LRRC15, in sarcomas and other advanced solid tumors. Clin Cancer Res. 2021;27(13):3556-3566. doi:10.1158/1078-0432.CCR-20-4513