Uterine sarcoma is a rare form of cancer that originates in the supportive tissues or muscle of the uterus, rather than the organ’s lining. This malignancy represents less than 10% of all uterine cancers. Because it arises from mesenchymal tissues, such as muscle and connective tissue, uterine sarcoma often behaves differently and requires unique approaches to diagnosis and treatment compared to the more prevalent endometrial cancers. Understanding this disease is important due to its aggressive nature.
Defining Uterine Sarcoma and Its Subtypes
Uterine sarcomas are a group of cancers that arise from the myometrium (muscular wall) or the connective tissue (stroma) of the uterus. This group is heterogeneous, including several distinct diseases with varying origins, behaviors, and treatment sensitivities. Distinguishing between these subtypes is crucial for determining prognosis and the appropriate therapeutic plan.
The most common subtype is Uterine Leiomyosarcoma (ULMS), accounting for 60% to 70% of all uterine sarcomas. ULMS originates from the smooth muscle cells of the myometrium and is known for its tendency to grow and spread quickly. This aggressive behavior often leads to a guarded prognosis.
Another major category is Endometrial Stromal Sarcoma (ESS), which develops from the connective tissue cells of the endometrium. ESS is classified into low-grade and high-grade forms based on cellular appearance and growth rate. Low-grade ESS typically grows slowly, often leading to a better prognosis than ULMS.
Low-grade ESS tumors frequently express hormone receptors, making them responsive to hormonal therapies. High-grade ESS is often grouped with Undifferentiated Uterine Sarcoma (UUS), characterized by highly abnormal cells and a much faster growth rate. UUS is the rarest and most aggressive subtype, often presenting at an advanced stage.
Recognizing the Warning Signs
The signs of uterine sarcoma are often vague. The most frequent symptom is abnormal vaginal bleeding, including bleeding between menstrual periods or any bleeding occurring after menopause. Postmenopausal bleeding should always prompt immediate medical evaluation.
Patients may also notice an unusual, non-bloody vaginal discharge. As the tumor grows, it can cause pelvic pain, abdominal discomfort, or a persistent feeling of fullness or bloating in the lower abdomen. The pressure from the growing mass may become severe enough that a lump can be felt during a physical examination.
The mass can also press on nearby organs, leading to changes in bladder and bowel function, such as frequent urination or constipation. While these symptoms can be caused by many benign gynecologic conditions, their persistence or sudden onset necessitates an evaluation to rule out uterine sarcoma.
Identifying Risk Factors
Uterine sarcomas are not primarily driven by hormonal factors like those linked to endometrial carcinoma (obesity and high estrogen exposure). The most significant known risk factor is a history of prior radiation therapy to the pelvis for another cancer. Sarcoma development following radiation often occurs many years later, typically five to twenty-five years after the initial treatment.
Another factor is the use of tamoxifen, a drug commonly prescribed to treat or prevent breast cancer. Although the increased risk is small, it is a recognized association, with sarcomas sometimes appearing two to five years after beginning therapy.
Rare genetic conditions can also predispose an individual to uterine sarcoma. These include congenital retinoblastoma, which increases the risk of soft tissue sarcomas. Similarly, Hereditary Leiomyomatosis and Renal Cell Cancer (HLRCC) syndrome, a rare family cancer syndrome linked to kidney cancer, is associated with an increased risk of uterine sarcomas.
Diagnosis and Staging
Diagnosing uterine sarcoma is challenging because the tumors often resemble benign growths called leiomyomas (fibroids) on initial imaging. The malignancy is frequently diagnosed unexpectedly after surgery performed for a presumed benign condition. Preoperative diagnostic tools can increase suspicion of sarcoma, but they are often not definitive.
Imaging techniques like magnetic resonance imaging (MRI) and computed tomography (CT) scans help visualize the mass, determine its size and location, and check for signs of spread. However, definitive diagnosis requires a tissue biopsy, usually obtained from tissue removed during surgery. Pathologists analyze the tissue to confirm the presence of sarcoma cells and identify the specific subtype.
The cancer is assigned a stage using the International Federation of Gynecology and Obstetrics (FIGO) staging system. This system classifies the extent of the cancer from Stage I (confined to the uterus) up to Stage IV (spread to distant organs). Staging is based on the tumor’s size, extent, spread to lymph nodes, and metastasis, directly dictating the prognosis and guiding the treatment plan.
Treatment Modalities
The cornerstone of treatment for localized uterine sarcoma is surgery, typically involving a total hysterectomy (removal of the uterus and cervix). Both fallopian tubes and ovaries are often removed (bilateral salpingo-oophorectomy), especially for postmenopausal individuals or those with high-grade sarcoma. The primary goal of surgery is to remove all visible cancerous tissue.
Surgery may be followed by additional (adjuvant) therapies depending on the cancer’s subtype and stage. For high-grade tumors like ULMS, chemotherapy is often recommended after surgery to target cancer cells that may have traveled beyond the uterus. Chemotherapy can also be used before surgery (neoadjuvant therapy) to shrink large tumors.
Radiation therapy uses high-energy rays to destroy cancer cells and may be used after surgery to reduce the risk of pelvic recurrence. Hormonal therapy may be used in specific circumstances, such as for hormone-sensitive, low-grade ESS. Treatment relies on a multidisciplinary team to determine the best sequence of surgery, chemotherapy, radiation, and hormone therapy.