Mucinous carcinoma is an uncommon form of cancer defined by the production of mucin, the primary protein component of mucus. The cancer cells form a gelatinous tumor where clusters of tumor cells appear to be floating in pools of extracellular mucus. This type of cancer can develop in any part of the body containing mucus-producing cells.
This cancer is divided into two primary subtypes: pure and mixed. Pure mucinous carcinoma consists almost exclusively of cancer cells suspended in mucin. In contrast, mixed mucinous carcinoma contains elements of the mucinous tumor alongside components of another cancer type, such as invasive ductal carcinoma in the breast. This distinction is a significant factor in determining the tumor’s behavior and outlook.
Common Locations and Associated Signs
Mucinous carcinoma is most frequently diagnosed in the breast, accounting for 1-7% of all breast cancers. It often presents as a palpable lump that may feel soft or rubbery upon examination. Other signs can include:
- Changes in breast size or shape
- Skin dimpling or puckering
- Nipple discharge
- Pain in the breast or armpit area
Due to its consistency, the tumor can sometimes grow to a significant size before being detected.
The colorectal region, including the colon and rectum, is another area where these tumors can arise. Signs associated with colorectal mucinous carcinoma are similar to other types of colon cancer and may include changes in bowel habits like diarrhea or constipation, the presence of blood in the stool, and abdominal pain. Unexplained weight loss and weakness are also potential indicators.
Less commonly, mucinous carcinoma can be found in the ovaries, where it may lead to symptoms such as abdominal bloating, persistent pelvic or abdominal pain, and pressure. Other rare sites for this cancer include the lungs, pancreas, appendix, and skin. In the lungs, it might cause a chronic cough or chest pain, while on the skin, it can appear as a reddish, rounded bump, particularly on the eyelid.
Diagnosis and Pathological Features
The diagnostic process for mucinous carcinoma begins with the detection of an abnormality through a physical exam or an imaging test. For breast cancer, a mammogram might show a mass with circumscribed, lobular contours, while an ultrasound may reveal a complex mass with both solid and cystic components. In other locations, a CT scan or colonoscopy could identify a suspicious lesion.
A definitive diagnosis, however, requires a biopsy. During this procedure, a small sample of the suspicious tissue is removed and sent to a pathologist for microscopic analysis. This examination confirms the presence of cancer and identifies its specific type.
Under the microscope, the pathologist looks for the characteristic features of mucinous carcinoma: nests of tumor cells floating in abundant extracellular mucin. A part of this analysis is determining whether the tumor is pure or mixed. A tumor is classified as pure mucinous carcinoma if more than 90% of its composition is mucinous. If the mucinous component is between 10% and 90%, it is classified as a mixed tumor, which also contains elements of another cancer type.
Treatment Approaches
Treatment for mucinous carcinoma is tailored to the individual, based on factors like the tumor’s location, size, stage, and whether it is a pure or mixed type. The plan is developed by a multidisciplinary team of oncologists to address the unique characteristics of the cancer.
Surgery is a foundational treatment, with the goal of completely removing the tumor. Depending on the location and extent of the cancer, this could range from a lumpectomy for breast cancer to a colectomy for colorectal cancer. The surgeon will also assess nearby lymph nodes to see if the cancer has spread, which is less common in pure mucinous types.
Following surgery, other therapies may be recommended. Radiation therapy uses high-energy rays to eliminate any cancer cells that might remain in the local area, reducing the risk of recurrence. Systemic therapies, which treat the entire body, are also common. These can include chemotherapy, hormone therapy to block estrogen levels in hormone-receptor-positive breast cancers, and targeted therapies that attack specific vulnerabilities in the cancer cells.
General Prognosis and Outlook
The general outlook for patients with mucinous carcinoma is often more favorable when compared to other invasive cancers found in the same organ, particularly when the tumor is the pure type. Pure mucinous carcinomas tend to be less aggressive, grow more slowly, and are less likely to metastasize to the lymph nodes and other parts of the body.
The distinction between pure and mixed forms is a significant prognostic factor. Mixed mucinous carcinomas have a prognosis that more closely resembles that of the other, non-mucinous cancer component, which is often more aggressive. For instance, a mixed mucinous tumor in the breast that includes invasive ductal carcinoma will have an outlook more similar to that of the ductal carcinoma.
Ultimately, prognosis is not a certainty and depends on a combination of factors. The stage of the cancer at the time of diagnosis is one of the most important predictors of outcome. The tumor’s grade, which describes how abnormal the cells look, its specific location, and the patient’s overall health also play a part in determining the long-term outlook.