Uterine Smooth Muscle Tumour of Unkown Malignant Potenial and Its Diagnostic Dilemma Between Benign Leimyoma and Leiomyosarcoma - A case report.

Uterine Smooth Muscle Tumour of Unkown Malignant Potenial and Its Diagnostic Dilemma Between Benign Leimyoma and Leiomyosarcoma – A case report.

Dr. Nanigopal Bhattacharya, Dr. Anirban Datta, Dr. Chinmoyee Roy, Dr. Sourav Barik

Abstract :
Smooth muscle tumour is catergorized by its cytological atypia, mitotic activity, and coagulative tumour cell necrosis. Smooth muscle tumour of unknown malignant potential (STUMP) is a hetergenous group of tumours in between leiomyoma and leiomyosarcoma charecterized by its cytological atypia, high and variable mitotic count suspicious of its maligant nature but not meeting the exact criteria of malignancy as charecteristic absence of tumour cell necrosis. Histpathologically neither its benign nor its malignant and clinically the chance of recurrence is quite unpredictable. Here we report a case of STUMP in a 43 years female attending VIMS for dysfunctional uterine bleeding.

Introduction :
Smooth muscle tumours are catergorized by its histological features like cytological atypia, mitotic activity, and coagulative tumour cell necrosis into leiomyomas and leiomyosarcomas^[1]. Smooth muscle tumour of uncertain malignant potential, a heterogeneous group of tumours, fall between leiomyomas and leiomyosaromas^[2]. The term STUMP was firstly used in the literature by Kempson in 1973^[3]. According to World Health Organization classification an uterine SMT not diagnosed unequivocally as benign or malignant should be defined as STUMP^[4]. STUMP includes other terminology like atypical leiomyoma with limited experience or atypical leiomyoma, low risk of recurece ^[1]. The clinical course of STUMP is poorly understood. There is no uniform diagnostic criteria of STUMP, hence over diagnosis is a common problem^[5]. However a smooth muscle tumour not satisfying Standford criteria of leiomyosarcoma but with unusual combination of cellular atypia, mitotic activity and tumour cell necrosis should be a clue for diagnosing as a case of STUMP^[5]. STUMP is very slowly growing tumour with a very low rate of recurrence. A clinicopathological study was conducted by Joseph SY Ng et al.18 cases of STUMP all of which was disease free after 5 years of removal^[6]. Another study by Andrea DallAstaet al. with 8 cases of STUMP had one incidence of recurrence after 9 years of hysterectomy^[7].

Case Presentation :
A 43 years multipara female presented with history of dysfunctional uterine bleeding not contolled by medical management. Patient was normotensive, nondiabetic, euthyroid. No history of oral contraceptive pill or other drugs were found. No significant history of any past surgery was there.
On ultrasound whole abdomen a large intramural firboid was detected. Patient underwent a planned hysterectomy and bilateral salpingo-ophoorectomy. Specimen of uterus with bilateral adenexae and a separately removed fibroid were received.

Gross Examination :
The fibroid was 6.5cm x 4.5x 4cm in size. Outer surface was gray white and smooth. Cut surface was firm, gray white and whorled in appearance. No haemorrhagic, necrotic or calcified area was identified grossly.

Sections studied at 400Xshows marked neuclear pleomorphism, occassional mitotic figure and no tumour cell necrosis.

Microscopic Examination :
Sections from fibroid showed long intersecting bundles of oval to elongated pleomorphic cells with diffuse mild to moderate neuclear pleomorphism and hyperchromasia and eosinophilic fibrillary cytoplasm. Mitotic activity was less than 10/10HPF. Hyaline acellular areas in between cellular areas were also noted.

Impression :
Over all histopathological features were suggestive of Smooth Muscle Tumour Of Unknown malignant potential.

Discussion :
Uterine leiomyoma or fibroid is a very common benign neoplasm affecting 20% to 30% of woman in between 30 to 50 years age group^[8].Leiomyoma is supposed to be associated with high eastrogen and progesterone exposure and thus found commonly in reproductive age group. It is rare after menopause and in young adults^[9]. Histopathological diagnosis is very straight forward and usually not a very thought provoking job. However problem starts with atypical features. Atypical leiomyoma have mild to moderate nuclear pleomorhopism,no definite coagulative tumour cell necrosis. Despite the histopathological features are enough to be worried, most of the atypical leiomyoma behaves as benign tumours clinically. Although a long term follow up has not been done so far^[10]. Alternate several studies coined the term smooth muscle tumour of unkown malignant potential of those atypical leiomyoma which have enough pleomrphism, nuclear atypia and abnormal mitotic figure to be suscpicious enough about leiomyosarcoma but not satisfying the Standford Criteria of Leiomyosarcoma^[5].
However in grey zone between obvious leiomyoma and leiomyosarcoma other enitity like aytpical leiomyoma, cellular leiomyoma, mitotically active leiomyoma other than STUMP should be understood by a pathologist.
An atypical leiomyoma or symplastic leiomyoma is composed of aypical bizarre cells, giant cells. But no coagulative necrosis is seen and atypia is also seen focally^[12] A mitotically active leiomyoma shows increased mitotic count even exceeding 15/10HPF but lacks other features of coagulative necrosis and cellular atypia^[13].

So far immunohistochemistry is concerned. P16, p53 and ki67 is helpful in distinguishing between cellular leiomyoma, benign leiomyoma and leiomyosarcoma. However STUMP from benign leiomyoma and leiomyosarcoma is difficult to distinguish by means of immunohsitochemsitry^{[ 11]}.

Conclusion :
There is no definite proposed guideline and criteria till date for diagnosing STUMP. Hence it remained in a grey zone between benign and malignant smooth muscle tumour and as a diagnosis of exclusion from both side having a high chance of manual error from observer to observer variation. Further studies and follow up is needed to find exact diagnostic criteria for STUMP.

References

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