Which statement correctly distinguishes a benign fibroid (leiomyoma) from a leiomyosarcoma?

Distinguishing Leiomyosarcoma from Benign Fibroids

The correct answer is B: fibroid has homogeneous cellular structure. Benign leiomyomas display a homogeneous cellular architecture that is virtually indistinguishable from normal myometrium, whereas leiomyosarcomas exhibit marked cellular pleomorphism, frequent mitoses, and coagulative tumor necrosis 1.

Why Each Answer is Correct or Incorrect

Option A: Benign fibroids usually found in close proximity to another fibroid

• Partially true but not a distinguishing feature. While leiomyomas frequently occur as multiple nodules (up to 70% of women at menopause have multiple fibroids), leiomyosarcomas are usually solitary lesions 1.
• However, multiplicity is an unreliable distinguishing feature because some women have solitary fibroids and the presence of multiple masses does not exclude malignancy 1.
• This is not the best distinguishing characteristic.

Option B: Fibroid has homogeneous cellular structure ✓

• This is the correct answer. Benign leiomyomas display homogeneous cellular architecture virtually indistinguishable from normal myometrium 1.
• In contrast, leiomyosarcomas exhibit marked cellular pleomorphism, frequent mitoses (often >10 per 10 high-power fields), and coagulative tumor necrosis 1.
• Pseudosarcomatous leiomyomas show significant histological diversity both between tumors and within the same tumor, with areas indistinguishable from conventional leiomyoma 2.
• The homogeneous cellular structure is a reliable histopathologic feature that distinguishes benign from malignant smooth muscle tumors 1, 2.

Option C: Fibroid has polyclonal origin

• This is incorrect. Leiomyomas arise from clonal expansion of individual smooth muscle cells, making them monoclonal tumors 1, 3.
• Uterine leiomyomas are well-vascularized, benign, monoclonal tumors of the myometrium 4.
• Approximately one-third of leiomyomas have clonal chromosomal aberrations, though these are not consistent between individual leiomyomata even in the same woman 3.
• The monoclonal origin is a characteristic feature of fibroids, not polyclonal 4, 1.

Option D: Fibroid has distinct appearance on MRI

• This is incorrect. Conventional magnetic resonance imaging cannot reliably differentiate benign leiomyomas from leiomyosarcomas 1.
• While an advanced MRI diagnostic algorithm incorporating enlarged lymph nodes, peritoneal implants, high diffusion-weighted signal, and low apparent diffusion coefficient values achieved 98% sensitivity and 96% specificity in training datasets, this requires specialized protocols beyond standard MRI 1.
• Standard MRI alone does not provide a distinct appearance that reliably distinguishes benign from malignant smooth muscle tumors 1.

Key Distinguishing Features in Clinical Practice

Histopathologic criteria (gold standard):

• Homogeneous cellular architecture in leiomyomas versus cellular pleomorphism in leiomyosarcomas 1, 2
• Mitotic count: >10 mitoses per 10 high-power fields suggests malignancy 1, 5
• Coagulative tumor necrosis indicates leiomyosarcoma 1, 5
• Definitive diagnosis requires permanent histopathologic sections; frozen sections are insufficient for accurately counting mitoses 1, 5

Clinical risk factors:

• Age is critical: leiomyosarcomas comprise only 0.1% of all uterine tumors but 1.7% in women undergoing hysterectomy in their seventh decade 1, 5
• Postmenopausal women with growing masses are at higher risk 1