by Jason Wasserman MD PhD FRCPC
September 5, 2024
A smooth muscle tumour of uncertain malignant potential (STUMP) is a rare type of tumour that arises in the smooth muscle of the uterus. These tumours are considered “uncertain” because it is difficult to determine whether they are benign (non-cancerous) or malignant (cancerous) based on their appearance under the microscope. STUMP falls somewhere between a benign leiomyoma (fibroid) and a malignant leiomyosarcoma. While many STUMPs behave in a non-aggressive manner, some can recur or progress to a more aggressive form.
STUMP of the uterus is not considered cancerous, but its behaviour is unpredictable. It falls between a benign tumour, like a leiomyoma (fibroid), and a malignant tumour, like leiomyosarcoma. While many STUMPs behave indolently, there is a risk that some may recur or, in rare cases, progress to a more aggressive form.
Because of this uncertainty, patients diagnosed with STUMP are carefully monitored with follow-up exams and imaging to check for signs of recurrence or progression. Treatment decisions depend on the tumour’s features and the patient’s overall health.
The symptoms of STUMP are often similar to those of other uterine tumours, such as fibroids. They may include:
However, some women with STUMP may not have any noticeable symptoms, and the tumour may be found during imaging or surgery for another condition.
The exact cause of STUMP is not well understood. Like other smooth muscle tumours of the uterus, STUMP likely arises from genetic mutations in the smooth muscle cells of the uterine wall. These mutations lead to abnormal growth, but not enough to clearly classify the tumour as benign or malignant. Factors such as hormonal changes, age, and genetic predispositions may play a role in the development of STUMP, but more research is needed to fully understand the causes.
The diagnosis of STUMP is made through the examination of tumour tissue under a microscope. The tissue is typically obtained through a biopsy or surgery. Pathologists look for specific features to determine whether the tumour should be classified as STUMP rather than a benign leiomyoma or a malignant leiomyosarcoma. The diagnosis is based on a combination of factors, including the appearance of the cells, the number of mitotic figures (dividing cells), and the presence or absence of necrosis (dead cells).
A smooth muscle tumour of uncertain malignant potential (STUMP) is made up of smooth muscle cells, which are normally found in the wall of the uterus. These cells help the uterus contract during menstruation and childbirth. While there are no strict rules for diagnosing STUMP, pathologists classify a tumour as STUMP if it fits into one of the following groups. Each of these groups is based on specific characteristics seen under the microscope:
These four groups help pathologists determine how the tumour might behave in the future and whether additional treatment or close follow-up is needed.