A Serous Borderline Tumor (SBT) is an ovarian epithelial tumor classified as “borderline” because it occupies an intermediate category between a benign growth and a fully invasive cancer. While these tumors exhibit abnormal cellular growth and proliferation, the cells do not show the destructive invasion into the underlying tissue that defines malignancy. This classification indicates a significantly better long-term outlook compared to invasive ovarian carcinoma, but diagnosis requires a specialized understanding and a tailored approach to treatment and follow-up.
Defining the Serous Borderline Classification
The designation of a tumor as “borderline” is based on microscopic examination of the tissue by a pathologist. This classification, recognized by the World Health Organization (WHO), is also known as an Atypical Proliferative Serous Tumor. SBTs are the most common subtype of borderline ovarian tumors, accounting for about 50% to 55% of all cases. They are distinct from benign serous cystadenomas and invasive serous carcinoma.
The defining characteristic of an SBT is the presence of epithelial cell overgrowth with varying degrees of nuclear atypia. This abnormal growth remains confined to the surface of the tumor structure without invading the deeper ovarian tissue. This lack of destructive invasion is the singular feature preventing classification as an invasive carcinoma.
SBTs often originate from benign precursors and share molecular alterations with Low-Grade Serous Carcinomas (LGSC). Genetic analysis frequently shows mutations in genes like KRAS and BRAF, distinct from those seen in high-grade ovarian cancers. The standard SBT is slow-growing, but the micropapillary variant is considered more aggressive and is sometimes equated with non-invasive LGSC.
SBTs may be associated with extra-ovarian spread, present in about 35% of cases as peritoneal implants. These implants are classified as either non-invasive or invasive, with the invasive type having a poorer prognosis. The presence and type of these implants are important factors used by the pathologist to determine classification and guide clinical management.
Identifying and Diagnosing Borderline Tumors
Serous Borderline Tumors are often discovered incidentally during imaging, as many patients may not experience symptoms. When symptoms do occur, they are typically non-specific, such as pelvic pain or pressure, abdominal swelling, or a feeling of fullness. The average age of diagnosis is younger than for invasive ovarian cancer, often presenting in women between 34 and 40 years old.
The initial diagnostic workup begins with pelvic imaging, such as a transvaginal ultrasound, to characterize the ovarian mass. SBTs can have characteristic imaging features, such as cystic lesions with papillary projections. MRI or CT scans may be used to further characterize the mass, assess for signs of spread, and help differentiate the tumor from other conditions.
The definitive diagnosis requires surgical removal of the mass followed by a histopathological examination. During surgery, a tissue sample may be analyzed immediately via a frozen section, but the final diagnosis is confirmed by a pathologist reviewing fixed and stained sections. This microscopic review confirms the lack of destructive stromal invasion and determines the classification.
Primary Treatment Options and Surgical Management
Surgery is the primary treatment for nearly all Serous Borderline Tumors, tailored to the patient’s age and desire for future fertility. The main goal is the complete removal of all visible tumor tissue, which provides both the definitive diagnosis and the treatment. Standard SBTs are generally considered resistant to chemotherapy or radiation, making surgical excision the sole therapeutic intervention.
For younger patients seeking fertility preservation, a fertility-sparing approach is recommended. This management may involve an ovarian cystectomy, where only the tumor is peeled away, or a unilateral salpingo-oophorectomy, which removes the affected ovary and fallopian tube. While conservative surgery carries a higher risk of recurrence, these recurrences are often borderline and can frequently be managed with a second conservative surgery.
For patients not seeking fertility preservation, the standard definitive surgery involves a hysterectomy and bilateral salpingo-oophorectomy, removing the uterus, cervix, and both ovaries and fallopian tubes. All patients undergo a comprehensive surgical staging procedure to check for tumor implants outside the ovary. This staging typically includes peritoneal washings, omentectomy, and biopsies of the peritoneal surfaces to determine the FIGO stage and guide post-operative surveillance.
Long-Term Prognosis and Required Surveillance
The prognosis for a Serous Borderline Tumor is positive, with survival rates reported to be approximately 95% at 10 years for all stages. This favorable prognosis reflects the slow-growing nature of the tumor and its non-invasive status, which differs significantly from invasive ovarian carcinoma. The prognosis is slightly less favorable for patients who present with advanced-stage disease or those with high-risk features, such as the micropapillary variant or invasive peritoneal implants.
Following initial treatment, patients require a long-term surveillance regimen to monitor for potential recurrence. The overall risk of recurrence is low (2% to 24%) and is more likely after fertility-sparing surgery. Most recurrences are borderline tumors, but a small percentage may progress to invasive low-grade serous carcinoma, necessitating close follow-up.
Surveillance involves regular clinical and pelvic examinations, along with periodic imaging, such as transvaginal ultrasound. Monitoring of tumor markers, such as CA-125, may also be included, though their role in follow-up is debated. The frequency of appointments decreases over time, but long-term monitoring is maintained indefinitely due to the possibility of late recurrence.