An unresectable desmoid tumour demonstrating long-term complete response to imatinib monotherapy: a case report

INTRODUCTION: Desmoid tumours are rare locally invasive soft tissue neoplasms arising from mesenchymal tissue that lack metastatic potential but have a high propensity for local recurrence. For unresectable mesenteric desmoid tumours requiring systemic therapy, the therapeutic landscape spans anti-hormonal combinations, chemotherapy, tyrosine kinase inhibitors, and gamma-secretase inhibitors. Imatinib is a multi-target tyrosine kinase inhibitor targeting PDGFR-alpha/beta and c-KIT that has demonstrated clinical activity in desmoid tumours with a favourable toxicity profile. CASE PRESENTATION: We present a case of a 27-year-old white Australian man who presented with a large abdominal mass and weight loss. Imaging revealed a 23 × 12 × 21 cm mass that was diagnosed as a desmoid tumour via biopsy. The tumour was deemed to be unresectable and radiotherapy was considered to carry an unacceptable risk of toxicity. Initial treatment with tamoxifen and sulindac was unable to halt disease progression. The patient was subsequently commenced on imatinib 400 mg daily. Imaging after four months showed partial response, and over six years, complete radiological remission was achieved despite intermittent medication compliance. Aside from one episode of grade 1 photosensitivity, no significant toxicities were observed. Imatinib was self-ceased after ten years of treatment, and the patient remains disease-free at eleven years post-diagnosis under active surveillance. CONCLUSION: We describe a case of complete and durable remission achieved with imatinib monotherapy in an unresectable mesenteric desmoid tumour with the patient remaining disease-free at 10 years. This case highlights the potential for long-term complete response and underscores the need for prospective data to guide treatment duration and cessation criteria.