Uterine sarcomas

Overview

• Rare, a heterogeneous group accounting for ~3 to 4% of uterine cancers. Distinct from endometrial carcinoma.
• Malignant mesenchymal subtypes:
  • Leiomyosarcoma (uLMS): most common (~60%). Often found incidentally at hysterectomy for presumed fibroids.
  • Low-grade endometrial stromal sarcoma (LG-ESS): indolent, ER+/PR+. JAZF1-SUZ12 fusion typical.
  • High-grade ESS (HG-ESS): YWHAE-NUTM2 or BCOR alterations.
  • Undifferentiated uterine sarcoma (UUS): hormone-receptor negative, aggressive.
  • Adenosarcoma: mixed mesenchymal plus benign epithelial; generally lower grade unless sarcomatous overgrowth.
  • Other: PEComa (perivascular epithelioid cell tumor).
• Carcinosarcoma is NOT a sarcoma: it is a poorly differentiated (metaplastic) carcinoma with malignant epithelial and mesenchymal elements, poor prognosis. All patients need optimal cytoreduction (fertility-sparing surgery not an option) and adjuvant carboplatin/paclitaxel; HER2+ advanced/recurrent disease: consider HER2-directed therapy (trastuzumab deruxtecan; trastuzumab + carbo/paclitaxel data strongest in uterine serous carcinoma), not routine adjuvant in all HER2+ carcinosarcoma. Consider RT for local control in RT-sensitive disease.

Workup

• No reliable preoperative markers distinguish sarcoma from benign leiomyoma; definitive diagnosis requires surgical pathology.
• Avoid morcellation if sarcoma suspected (FDA warning: risk of intraperitoneal seeding).
• Imaging: MRI may suggest sarcoma; PET sometimes useful.

Leiomyosarcoma (uLMS)

• High recurrence risk (~70%) even in uterine-confined tumors. Surgery (total hysterectomy) is standard; BSO usual but ovarian preservation can be considered in premenopausal uterus-confined uLMS. LN dissection generally not required.
• Adjuvant chemo or RT has no demonstrated recurrence-free or OS benefit in uterine-confined uLMS; observation is standard. For stage II to III consider adjuvant systemic therapy and/or RT, or observation (especially with negative margins). Gemcitabine + docetaxel adjuvant was controversial; the randomized GOG-0277 trial (gem/doc then doxorubicin vs observation) closed for poor accrual with no survival benefit (SARC005 was a single-arm phase 2).
• Locoregional recurrence: repeat surgery with or without RT.
• Advanced/metastatic 1L: anthracycline-based, doxorubicin + trabectedin or doxorubicin alone; gemcitabine + docetaxel (Hensley regimen) is a typical alternative.
• LMS-04 (Pautier Lancet Oncol 2022; NCT02997358): phase 3 doxorubicin + trabectedin vs doxorubicin alone, 1L metastatic uterine/soft-tissue LMS. mPFS 12.2 vs 6.2 mo (HR 0.41); mOS ~33 vs ~25 mo (HR 0.65, overall population; mature OS, NEJM 2024). Regimen: doxorubicin + trabectedin x6 then trabectedin maintenance. New 1L option at experienced centers; heavier toxicity (myelosuppression, transaminitis).
• Other active agents (if not used earlier): doxorubicin, gemcitabine, ifosfamide, trabectedin, pazopanib, dacarbazine, eribulin.
• Biomarker-directed: pembrolizumab for MSI-H/dMMR (rare in uLMS) or TMB-high tumors after prior therapy with no satisfactory alternatives; PARP inhibitors (olaparib, rucaparib, niraparib) as 2L options for BRCA2-altered uLMS.

Endometrial stromal sarcoma (LG-ESS)

• Low-grade, indolent, ER+/PR+; 10-year OS >90%. Stage I: surgery then observation. Stage II-IV: adjuvant endocrine therapy (AI or progestin).
• Hormone therapy is the mainstay for recurrence: aromatase inhibitor (letrozole, anastrozole) preferred, or progestin. Avoid estrogen.
• Extended AI with or without CDK4/6 inhibitor (retrospective 2024 data): sustained responses to letrozole even in metastatic LG-ESS; ribociclib/palbociclib combinations being explored given cyclin/CDK signaling in ESS.
• Surgical resection of resectable recurrence.

HG-ESS, UUS, adenosarcoma, PEComa

• HG-ESS: receptor status varies by subtype (often negative, esp. YWHAE-NUTM2); UUS variable; both aggressive. Doxorubicin-based or gemcitabine + docetaxel per soft-tissue sarcoma guidelines; encourage clinical trials.
• Adenosarcoma: managed like LG-ESS; with sarcomatous overgrowth it is high-risk and driven by the high-grade component. Surgery is primary; Stage I without sarcomatous overgrowth: observe. Higher-stage or sarcomatous overgrowth: consider adjuvant systemic therapy and/or RT (treat as high-grade sarcoma).
• PEComa: nab-sirolimus (albumin-bound) is a 1L option; sirolimus, everolimus, temsirolimus are off-label mTOR alternatives (e.g., if nab-sirolimus unavailable), not a defined 2L after nab-sirolimus.

Survivorship

• Follow-up is similar to endometrial cancer, including periodic chest imaging as for soft-tissue sarcomas.
• Do NOT offer estrogen replacement (HRT) in LG-ESS survivors because these tumors are ER/PR positive and estrogen can stimulate them.

High-yield uterine sarcoma pearls

• Avoid morcellation if uLMS is possible.
• uLMS: doxorubicin (with or without trabectedin) or gemcitabine + docetaxel; surgery is the mainstay; adjuvant therapy has no proven survival benefit.
• LG-ESS: hormone therapy (AI); avoid estrogen replacement.
• Carcinosarcoma is a carcinoma, not a sarcoma: carbo/paclitaxel (HER2+ advanced/recurrent: consider HER2-directed therapy; not routine adjuvant).