Mucinous Ovarian Cancer: Understanding This Rare but Distinct Subtype

Mucinous ovarian cancer is a rare and unique form of epithelial ovarian cancer that behaves very differently from other ovarian cancer types. 

While it represents only about 2 to 3% of all ovarian cancers, understanding its distinct characteristics is crucial for patients, families, and healthcare providers navigating this diagnosis.

Unlike the more common high-grade serous ovarian cancers that affect older women, mucinous ovarian cancer typically strikes younger patients and presents with its own set of challenges and opportunities. 

While both mucinous and low-grade serous ovarian cancer can affect younger women, they are biologically distinct diseases with different cellular origins, molecular characteristics, and treatment responses. This guide will help you understand what mucinous ovarian cancer is, how it’s diagnosed, and what treatment options are available.

What Is Mucinous Ovarian Cancer?

What is mucinous ovarian cancer, exactly? This type of cancer develops when cells in the ovaries that produce mucin — a thick, protective substance normally found in the digestive and respiratory systems — become malignant. The tumors are literally filled with this mucus-like fluid, which is how they get their name.

These cancers fall under the broader category of epithelial ovarian cancer, but they’re fundamentally different from other subtypes. While most ovarian cancer cases are high-grade serous carcinomas, mucinous ovarian cancers have their own molecular signature, treatment response patterns, and prognosis.

One of the most striking features of mucinous ovarian tumors is their size. The average tumor measures about 18 centimeters at diagnosis — roughly the size of a cantaloupe. Some can grow even larger, occasionally filling the entire abdominal cavity.

The true incidence of primary mucinous ovarian cancer is much lower than originally thought. Earlier estimates suggested it comprised 6 to 25% of ovarian cancers, but careful pathological review has revealed the actual percentage is closer to 2.4%. 

This dramatic revision occurred because many tumors previously classified as primary mucinous ovarian cancers were actually metastases from other organs, particularly the gastrointestinal tract.

The Challenge of Primary vs. Metastatic Disease

One of the biggest diagnostic challenges with mucinous ovarian tumors is determining whether they started in the ovary or spread there from somewhere else. Studies show that approximately 80% of mucinous ovarian tumors are actually metastatic, meaning they originated in another organ.  

The most common primary sites that can metastasize to the ovary include:

• Gastrointestinal tract (45%)
• Pancreas (20%)
• Cervix and endometrium (18%)
• Breast (8%)

This distinction matters enormously because primary and metastatic mucinous cancers are treated completely differently. Primary ovarian tumors tend to be larger, unilateral (affecting only one ovary), and have a better prognosis when caught early.

Mucinous Ovarian Cancer: Symptoms and Diagnosis

The symptoms of mucinous ovarian cancer often appear earlier than those of other ovarian cancer types, primarily because these tumors grow so large. Many women notice symptoms when the mass becomes large enough to cause physical discomfort or visible abdominal changes.

Common Symptoms

The most frequently reported symptoms include:

• Abdominal bloating or distension (often the first noticeable sign)
• A palpable lump on one side of the abdomen
• Pelvic or abdominal pain that may be persistent or intermittent
• Feeling full quickly after eating small amounts
• Weight gain from the tumor mass itself
• Frequent or urgent urination from pressure on the bladder
• Fatigue and general discomfort

Unlike many other forms of ovarian cancer, these symptoms often develop while the disease is still in early stages. This is actually good news, as it can lead to earlier detection and better outcomes.

The Diagnostic Process

When mucinous ovarian cancer is suspected, the diagnostic workup is comprehensive and includes several important steps.

Physical Examination: Your doctor will perform a thorough pelvic exam to feel for masses and assess the size and characteristics of any tumors found.

Imaging Studies:

• Transvaginal or pelvic ultrasound to visualize the ovaries
• CT scans to evaluate the extent of disease
• MRI may provide additional details about the tumor’s characteristics

Blood Tests: Unlike other ovarian cancers where CA-125 is often elevated, mucinous ovarian cancers more commonly show elevation in:

• CEA (carcinoembryonic antigen): elevated in 88% of mucinous cases vs. only 19% of other ovarian cancers 
• CA19-9
• CA-125 is usually normal or only mildly elevated

Gastrointestinal Evaluation: Because so many mucinous ovarian tumors are actually metastases from GI sources, your gynecologic oncologist may recommend colonoscopy or upper endoscopy to rule out a primary tumor elsewhere.

Tissue Biopsy: The definitive diagnosis requires examination of tumor tissue, usually obtained during surgery. The pathologist will look for specific characteristics that distinguish primary mucinous ovarian cancer from metastatic disease.

How Is Mucinous Ovarian Cancer Treated?

Treatment for mucinous ovarian cancer depends heavily on the stage at diagnosis, whether it’s truly primary to the ovary, and the patient’s individual circumstances. 

The good news is that most cases — about 80% — are diagnosed at stage I, when the cancer is still confined to the ovary. 

Surgical Treatment

Surgery forms the cornerstone of ovarian cancer treatment for mucinous tumors, just as it does for other types. However, there are some important differences in surgical approach.

Primary Surgery Goals:

• Complete removal of the tumor without rupture (spillage can affect prognosis)
• Thorough staging to determine the extent of the disease
• Preservation of fertility when appropriate and safe

Staging Procedures: For mucinous ovarian cancers, staging typically includes:

• Removal of the affected ovary and fallopian tube
• Peritoneal washings to check for cancer cells
• Omentectomy (removal of the omentum)
• Peritoneal biopsies from multiple sites
• Inspection of the entire abdominal cavity

Importantly, routine lymph node removal is generally not recommended for early-stage mucinous ovarian cancers. 

Multiple studies have shown that mucinous tumors confined to the ovary have essentially zero risk of lymph node involvement—a stark contrast to serous ovarian cancers where 10% of apparent stage I cases have positive lymph nodes.  

The Role of Appendectomy

The question of whether to remove the appendix during surgery for mucinous ovarian tumors has evolved over time. Current recommendations suggest that appendectomy should be performed if:

• The appendix appears abnormal during surgery
• There are signs of pseudomyxoma peritonei (mucin throughout the abdomen)
• The surgical team suspects the tumor might be metastatic from an appendiceal source

However, routine appendectomy is no longer recommended if the appendix appears normal, as studies have shown minimal benefit in these cases.

Fertility-Sparing Surgery

Because mucinous ovarian cancers often affect younger women and are typically unilateral, fertility-sparing surgery is frequently possible. This approach involves removing only the affected ovary and fallopian tube while preserving the uterus and contralateral ovary.

This option is appropriate for:

• Women of reproductive age who desire future fertility
• Stage I disease that appears confined to one ovary
• Absence of suspicious findings in the contralateral ovary or elsewhere

Studies have shown that fertility-sparing surgery doesn’t compromise outcomes when performed appropriately, with excellent survival rates maintained.

Chemotherapy Considerations

The role of chemotherapy in mucinous ovarian cancer is one of the most challenging aspects of treatment. Unlike other ovarian cancer types, mucinous tumors have notably poor response rates to standard platinum-based chemotherapy.

The role of chemotherapy varies dramatically by stage. For early-stage disease, the benefit of adjuvant chemotherapy remains unclear, with studies showing no clear survival advantage. However, advanced mucinous ovarian cancers face a significant challenge: they’re notably resistant to standard platinum-based chemotherapy that works well for other ovarian cancer types, leading to much poorer outcomes when the disease has spread.

Targeted Therapy and Future Directions

The molecular profile of mucinous ovarian cancers opens doors for targeted therapy approaches:

KRAS Mutations: Present in 33 to 46% of mucinous ovarian cancers, these mutations are targets for emerging therapies.

HER2 Amplification: This could make anti-HER2 therapies like trastuzumab potentially beneficial for some patients.

EGFR Expression: Elevated in many mucinous tumors, suggesting potential for anti-EGFR therapies in carefully selected patients.

Small studies have shown promising results with targeted approaches, but larger trials are needed to establish their role in treatment.

Mucinous Ovarian Cancer Prognosis and Outlook

The prognosis for mucinous ovarian cancer depends heavily on the stage at diagnosis and whether it’s truly primary to the ovary.

Early-Stage Disease: Patients with stage I mucinous ovarian cancer have excellent outcomes, with 5-year survival rates exceeding 90%. The expansile subtype generally has better outcomes than the infiltrative subtype.

Advanced-Stage Disease: Unfortunately, the outlook for advanced mucinous ovarian cancer is significantly worse than for other ovarian cancer types. Median overall survival for advanced disease ranges from 12 to 30 months, compared to much longer survival times for advanced serous cancers.

The key factors affecting prognosis include:

• Stage at diagnosis (most important factor)
• Completeness of surgical resection
• Histologic subtype (expansile vs. infiltrative)
• Response to chemotherapy

Important note: Ovarian cancer survival rates have been improving steadily over the years due to advancements in treatment. While these rates are based on large population studies and serve as a general guide, they don’t necessarily reflect individual situations, and they do not definitively predict any one person’s journey with ovarian cancer. 

A gynecologic oncologist should be able to answer the patient’s questions and make a more accurate prognosis. They can also provide a more accurate assessment by taking into account personal circumstances and creating a tailored treatment plan. Factors such as the specific type of ovarian cancer, stage at diagnosis, overall health, and response to treatment all play a role in determining a person’s unique prognosis. With the support of a medical team and loved ones, individuals can navigate this challenging time with strength and resilience.

The Importance of Expert Care

Given the complexity of diagnosing and treating mucinous ovarian cancer, expert care is essential. A gynecologic oncologist with experience in rare ovarian cancer subtypes can provide:

• Accurate diagnosis and staging
• Appropriate surgical planning
• Access to clinical trials for novel treatments
• Multidisciplinary care coordination

The rarity of mucinous ovarian cancer means that many general oncologists may see very few cases throughout their careers. Seeking care at a comprehensive cancer center with gynecologic oncology expertise can make a significant difference in outcomes.

Moving Forward with Hope

While mucinous ovarian cancer presents unique challenges, there are reasons for optimism. The fact that most cases are diagnosed early provides an opportunity for a cure with appropriate treatment. Additionally, growing understanding of the molecular characteristics of these tumors is opening new avenues for targeted therapies.

For patients and families facing a mucinous ovarian cancer diagnosis, connecting with specialized care teams and support networks can provide both medical expertise and emotional support throughout the journey. While the path may be different from more common ovarian cancers, there is hope for positive outcomes, especially with early detection and appropriate treatment.