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Leiomyosarcomas

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1. Epidemiology

• Peak incidence is in the 6th and 7th decades of life.
• Retroperitoneal and uterine LMS are more common in females; other sites show a male predominance.
• Predisposing risk factors include prior radiation exposure and immunosuppression (particularly Epstein-Barr virus-related tumor promotion in post-transplant patients).
• Leiomyoma (the benign counterpart) is NOT a precursor to leiomyosarcoma.

• Sabiston Textbook of Surgery, p. 2975

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2. Sites of Origin

• Robbins, Cotran & Kumar Pathologic Basis of Disease; Sabiston Textbook of Surgery

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3. Pathogenesis & Molecular Biology

• Arise from smooth muscle cells or their precursors (e.g., myometrial cells or endometrial stromal precursor cells for uterine LMS).
• Possess complex, highly variable karyotypes with numerous chromosomal deletions and instability - no single pathognomonic marker.
• Key molecular alterations include mutations in TP53, RB, and PTEN (tumor suppressor genes).
• A subset (~30%) contains MED12 mutations, a genetic aberration otherwise largely unique to uterine smooth muscle tumors (both leiomyomas and LMS).

• Robbins & Kumar Basic Pathology, p. 679-683; Robbins, Cotran & Kumar PBD, p. 3047

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4. Morphology

Gross Pathology

• Typically soft, fleshy, hemorrhagic, necrotic masses.
• Uterine LMS grows as either:
  • Bulky masses invading the uterine wall, or
  • Polypoid masses projecting into the uterine lumen.
• Deep soft tissue LMS are firm, rubbery, or fleshy tumors, often well-circumscribed with a cystic/necrotic center.

Histology

• Cases impossible to classify definitively are called STUMP (Smooth muscle tumor of uncertain malignant potential).

• Robbins, Cotran & Kumar PBD, p. 3052-3054; Robbins & Kumar Basic Pathology, p. 688

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5. Immunohistochemistry

• Desmin ✓
• Smooth muscle actin (SMA) ✓
• h-Caldesmon ✓
• Calponin ✓

• Sabiston Textbook of Surgery; Andrews' Diseases of the Skin, p. 1585

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6. Grading: FNCLCC System

• Mulholland and Greenfield's Surgery, p. 2817 (FNCLCC Table)

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7. Staging

Soft Tissue Sarcoma (AJCC 8th edition) - Trunk & Extremity LMS

Uterine LMS: FIGO Staging (2009)

• Berek & Novak's Gynecology; SCHWARTZ'S PRINCIPLES OF SURGERY

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8. Clinical Features

• Presentation: Painless firm mass (deep LMS); abdominal symptoms in retroperitoneal tumors; abnormal uterine bleeding or pelvic mass in uterine LMS.
• Some uterine LMS are found incidentally at hysterectomy performed for presumed leiomyoma.
• Metastasis: Predominantly hematogenous - most common sites are lung, liver, bone, and brain; abdominal dissemination also occurs.
• Lymph node metastases are uncommon.

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9. Cutaneous/Superficial LMS (Special Form)

• Accounts for ~2% of all STS.
• Two subtypes differ significantly in prognosis:

• Association with Reed syndrome (hereditary leiomyomatosis and renal cell cancer - HLRCC) has been reported; caused by fumarate hydratase (FH) gene mutations.
• Histologically: dense cellularity, nuclear pleomorphism, numerous mitoses, disarray of smooth muscle bundles.
• Treatment: wide local excision with 1-cm margin; Mohs surgery to limit recurrence (~15% recurrence rate).

• Andrews' Diseases of the Skin, p. 1583-1587; Fitzpatrick's Dermatology, p. 1882

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10. Treatment

Surgery (Primary Modality)

• Macroscopically complete resection is the cornerstone of treatment for all LMS.
• Uterine LMS: Total abdominal hysterectomy (TAH) with bilateral salpingo-oophorectomy (BSO). Lymphadenectomy is not routinely required.
• Retroperitoneal LMS involving IVC: Options include tumor resection with IVC ligation or reconstruction (patch/interposition graft). For infrahepatic IVC involvement, ligation without reconstruction may be acceptable if collaterals are preserved.

Adjuvant Therapy

• Routine adjuvant chemotherapy or radiation after resection is not currently recommended (subject of ongoing trials, including the EORTC STRASS-2 study).
• Neoadjuvant chemotherapy may be considered for large retroperitoneal tumors.

Systemic Treatment for Advanced/Metastatic Disease

• Doxorubicin (backbone agent)
• Ifosfamide
• Gemcitabine + Docetaxel (particularly effective in uterine LMS)
• Trabectedin (approved in Europe for LMS specifically)

Note: Olaratumab (anti-PDGFRα monoclonal antibody) combined with doxorubicin initially showed promise in Phase II but failed to improve overall survival in the Phase III ANNOUNCE trial and has been withdrawn from the market.

• Sabiston Textbook of Surgery, p. 2979-2983

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11. Prognosis

• More than one-half of all LMS eventually metastasize hematogenously.
• Retroperitoneal tumors are often diagnosed late due to large size and silent presentation.

• Robbins, Cotran & Kumar PBD, p. 3059; Robbins & Kumar Basic Pathology, p. 690

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Recent Literature (2024-2026)

• A 2025 systematic review and meta-analysis on spinal leiomyosarcoma (PMID 40368091, World Neurosurg) examined surgical outcomes in primary/metastatic spinal LMS - a rare but increasingly recognized metastatic site.
• A 2025 systematic review on retroperitoneal sarcoma (PMID 40465137, Curr Oncol Rep) covers current management strategies for retroperitoneal LMS and liposarcoma.
• A 2024 systematic review on Mohs surgery for superficial LMS (PMID 40526951, Dermatol Online J) reports ~15% recurrence with Mohs vs. higher rates with wide local excision, supporting Mohs as the preferred approach for cutaneous LMS.

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Large necrotic mass → Mitoses + atypia → SMA/Desmin positive → surgery first → hematogenous spread to Lung, Marrow, Spinal sites.

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Uterine Leiomyosarcoma (ULMS)

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1. Epidemiology & Risk Factors

• Median age at diagnosis: 54 years (range 43-63); can occur in women in their 20s
• More common in African American women, who also have a poorer prognosis
• Premenopausal women have better survival than postmenopausal women
• No strong relationship to parity
• Prior pelvic radiation in ~4% of cases
• The incidence of sarcomatous transformation within a benign leiomyoma is only 0.13-0.81% - most ULMS arise de novo, not from pre-existing leiomyomas
• Hereditary risk: Hereditary leiomyomatosis and renal cell cancer (HLRCC) syndrome - caused by fumarate hydratase (FH) gene mutations - confers an unknown but elevated risk; also linked to hereditary retinoblastoma (RB gene mutations)

• Berek & Novak's Gynecology, p. 1862; Fitzpatrick's Dermatology

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2. Pathogenesis & Molecular Biology

• Complex, variable karyotypes with chromosomal deletions and instability
• Key mutations: TP53, RB (retinoblastoma), PTEN (tumor suppressor)
• A subset contains MED12 mutations - an aberration otherwise largely unique to uterine smooth muscle tumors (shared with leiomyoma)
• Unlike endometrial carcinoma, ULMS has no association with unopposed estrogen exposure

• Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 3047

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3. Clinical Presentation

• Key clinical clue: Pelvic pain + rapidly enlarging uterus, especially in a postmenopausal woman - should raise strong suspicion for ULMS.
• Physical examination reveals a pelvic mass.
• Endometrial biopsy establishes diagnosis in up to one-third of cases (if submucosal).

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4. Imaging

• MRI (especially contrast-enhanced) is superior to ultrasound or CT in differentiating ULMS and STUMP from leiomyoma.
• Differentiating ULMS from degenerated leiomyoma can still be challenging on preoperative imaging - biopsy should be considered when diagnosis is uncertain.
• Diffusion-weighted MRI has been studied specifically for this distinction.

• Berek & Novak's Gynecology, p. 1868

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5. Pathology

Gross Morphology

1. Bulky, fleshy, hemorrhagic, necrotic masses invading the uterine wall
2. Polypoid masses projecting into the uterine lumen

Microscopic Criteria for Malignancy

Caveat: Mitotically active leiomyomas occur in young/pregnant women - caution required before diagnosing malignancy in this group.

Immunohistochemistry

• Desmin ✓
• Smooth muscle actin (SMA) ✓
• h-Caldesmon ✓

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6. FIGO Staging for Uterine LMS (2009)

• Berek & Novak's Gynecology; Prat J. FIGO staging for uterine sarcomas. Int J Gynecol Obstet 2009;104:177-178

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7. Pattern of Spread

1. Direct myometrial invasion → pelvic structures
2. Lymphovascular invasion → pelvic blood vessels and lymphatics → intra-abdominal dissemination
3. Hematogenous spread (most important) → lungs (most common distant site), bone, brain

• Lymph node metastasis is rare (<5% at diagnosis) in early-stage disease.

• Tumors >5 cm → poorer prognosis
• Infiltrating (vs. pushing) borders → poorer prognosis
• Extension beyond uterus → poorer prognosis

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8. Treatment

Surgery - Cornerstone of Management

• Total hysterectomy is the standard for uterine-confined disease.
• Bilateral salpingo-oophorectomy (BSO):
  • Mandatory in postmenopausal women
  • Mandatory with gross extrauterine disease
  • Ovarian preservation acceptable in premenopausal women with early-stage disease - does NOT increase recurrence risk
• Lymphadenectomy: NOT routinely recommended (no survival advantage given low nodal metastasis rate)
• Cytoreductive surgery / pulmonary metastasectomy may improve survival in advanced disease

⚠️ Morcellation Warning

• Berek & Novak's Gynecology, p. 1872; Schwartz's Principles of Surgery

Radiation Therapy

• Not recommended as adjuvant therapy.
• An EORTC phase III trial comparing adjuvant pelvic radiation vs. observation in early-stage ULMS showed no difference in overall survival or recurrence rates.
• SEER database data also does not support adjuvant radiation.

Chemotherapy

Note on Olaratumab: A Phase II trial showed improved OS with doxorubicin + olaratumab (OS 26.5 vs. 14.7 months). However, the Phase III ANNOUNCE trial failed to confirm overall survival benefit → olaratumab was withdrawn from the market.

• Berek & Novak's Gynecology, p. 1892; Schwartz's Principles of Surgery, p. 2257

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9. Prognosis

• More than half of all ULMS eventually metastasize hematogenously.
• Recurrence risk: 40-70% even after complete resection of early-stage disease.
• Late recurrences are characteristic, particularly in epithelioid and myxoid variants.

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10. Clinicopathologic Variants

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11. STUMP (Smooth Muscle Tumor of Uncertain Malignant Potential)

• Applied when tumors cannot be definitively classified as benign or malignant
• Mitotic index: 5-10 MF/10 HPF with or without atypia
• Less predictable behavior - requires close follow-up
• Treatment: hysterectomy; individualized adjuvant decisions

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Recent PubMed Evidence (2023-2026)

• A 2025 study on uterine leiomyosarcoma serial recurrences (PMID 41027098, Gynecol Oncol) provides NIH-funded molecular analysis of disease progression at each recurrence.
• A 2025 review on future targeted therapies for LMS (PMID 40410055, Hematol Oncol Clin North Am) covers emerging targets including CDK4/6 inhibitors, PARP inhibitors, and immunotherapy.
• A 2024 review on targeted therapy for leiomyosarcoma (PMID 38473300, Cancers) highlights that uterine LMS is uniquely chemosensitive among LMS subtypes, and discusses emerging targets.

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• ULMS = most common uterine sarcoma; arises de novo from myometrium
• Diagnosed by: mitoses ≥10/10 HPF + cytologic atypia + coagulative necrosis
• Surgery is the only curative treatment; avoid morcellation
• Adjuvant radiation and chemotherapy do NOT improve early-stage outcomes
• Gemcitabine + docetaxel is the most active regimen for advanced disease
• Overall prognosis is poor - 5-year survival ~47%, with 40-70% recurrence risk