Novel orthotopic uterine leiomyosarcoma model demonstrated enhanced tumor growth, metastasis, and chemosensitivity compared to subcutaneous counterparts

Objective: Uterine leiomyosarcoma (uLMS) maintains a poor prognosis due to its aggressive behavior and limited therapeutic response. Preclinical progress is severely hindered by traditional subcutaneous models that often fail to metastasize, despite one-third of uLMS patients displaying metastases at diagnosis. This study aimed to establish a reproducible, physiologically accurate orthotopic uLMS murine model that faithfully recapitulates disease progression and chemotherapeutic response.Methods: Primary subcutaneous tumors were established via SK-LMS-1 cell injections in NOD/SCID mice. Harvested xenografts were surgically implanted heterotopically (subcutaneous flank) or orthotopically (uterine myometrium). Eight days post-implantation, mice were randomized to receive intraperitoneal doxorubicin (1.2 mg/kg twice weekly) or vehicle control for three weeks. Tumor growth was tracked longitudinally via MRI (orthotopic) or caliper measurement (subcutaneous). Immunohistochemistry evaluated tumor vitality, microenvironment hypoxia, vascular density, and metastatic spread.Results: Orthotopic tumors exhibited significantly accelerated growth kinetics compared to subcutaneous counterparts. This expansion was supported by co-option of host uterine vasculature, resulting in ample tumor perfusion, suppressed tissue hypoxia, and robust proliferation. Crucially, 37% of primary orthotopic tumors developed spontaneous, multi-organ metastases to pulmonary, omental, and intraperitoneal sites by 4 weeks. Orthotopic tumors demonstrated heightened sensitivity to doxorubicin, achieving a 55% volume reduction compared to 44% in subcutaneous controls, mediated by superior intratumoral drug delivery supported by increased cleaved caspase-3-dependent apoptosis.Conclusions: Surgical orthotopic xenografting recapitulates clinical uLMS, demonstrating site-dependent vascular co-option, spontaneous systemic metastasis, and enhanced chemosensitivity. By mimicking physiological characteristics of human uLMS, this orthotopic model offers significant potential for enhancing understanding of uLMS and evaluating novel therapies.