[1154] Myxoid Smooth Tumors of the Uterus: Can Histology Predict Behavior?

Molly A Gurney, Anais Malpica, Elizabeth D Euscher. University of Texas MD Anderson Cancer Center, Houston, TX

Background: Myxoid smooth muscle tumors (MSMT) of the uterus are diagnostically problematic. Due to their rarity, their criteria for malignant behavior are not well defined with overlapping histologic features between clinically benign and malignant tumors. This clinicopathologic study represents the largest series of such cases to date.
Design: A 20 year search (1992-2012) of our pathology data base yielded 35 MSMT. 15 cases were excluded based on presence of conventional leiomyosarcoma (LMS) or containing <50% myxoid change. H&E slides were reviewed in all cases. The following parameters were recorded: patient (pt) age, stage of disease, tumor size, tumor border, % myxoid component, degree of cellularity, presence of coagulative tumor cell necrosis (CTCN), presence of marked atypia, mitotic index (MI), treatment and outcome.
Results: Pts ages ranged from 28 to 64 yrs (median 48) with 9 to 213 mos follow up (median 66) available for 16 pts. Stage of disease was known for 16 pts: Stage I, 13; Stage II, 3. 6 pts had a diagnosis of smooth muscle tumor of uncertain malignant potential (STUMP), and 14 pts had a diagnosis of LMS. 3 tumors had at least focally increased cellularity. 15 tumors had bland spindle cells, and 4 had epithelioid cells. Remaining pathologic features of cases with follow up by outcome are presented in Table 1;pathologic features by tumor diagnosis are presented in Table 2.

Features of Myxoid Smooth Muscle Tumors by Outcome
 Tumor Size (cm, median)Infiltrative Tumor Border Present% Myxoid (Median)LVI PresentCTCN PresentSevere Atypia PresentMI (median)
No Evidence of Disease (n=13)75803544
Recurrent/Dead of Disease (n=3)102901309.5

Pathologic Features of Myxoid Smooth Muscle Tumors By Diagnosis
 Tumor Size (cm, median)Infiltrative Border Present% Myxoid (Median)LVI PresentCTCN PresentSevere Atypia PresentMI (median)
STUMP (n=6)4177.51102
LMS (n=14)8.98903956

9 pts received treatment after surgery: chemotherapy, 6;radiation, 3. 3 pts recurred at these sites: pelvic 3; abdomen 1; lung, 1. No STUMPS recurred; 3/14 (21%) LMS recurred and died of disease.
Conclusions: MSMT are uncommon and occur over a wide age range. Recurrent and nonrecurrent MSMT have overlapping histologic features. Of recurrent MSMT, all had CTCN and two had an infiltrative border. Although there is a trend to increased MI in recurrent MSMT, one case had 1 mitosis. MI may not be a reliable predictor of malignant potential. Once MSMT with foci of conventional LMS are excluded, atypia may not be a reliable indicator of malignancy. Compared to conventional LMS, MSMT have a better outcome.
Category: Gynecologic & Obstetrics

Monday, March 4, 2013 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 176, Monday Morning


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