Introduction
Medullary carcinoma of the thymus, or MCT, is one of the extremely rare but unique tumors derived from the thymus - a small organ located in the anterior portion of the chest cavity. The thymus contains both benign and malignant tumors and is considered an important part of the immune system, mainly at the very early stages of life. Medullary carcinoma of the thymus is reviewed in this article by discussing clinical presentation, histopathological features, diagnostic considerations, treatment options, and prognosis.
What Is the Thymus and What Is Its Function?
The thymus is a vital organ of immunity, where T lymphocytes (T cells) develop. T cells are white blood cells that function as the central role in cell-mediated immunity and allow the body to resist infection and disease. The thymus is found in the anterior mediastinum (the region within the chest cavity situated between the lungs and above the heart) just below the breastbone. The thymus is very active during a person's childhood and adolescence period as it plays an important role in developing a full-fledged immune system during early life. After attaining puberty, the thymus begins shrinkage-a process termed involution-and so does its role throughout aging.
Nevertheless, the thymus is not exempt from diseases and cancers. Thymic carcinoma is one of the rare kinds of cancer starting from the epithelial cells inside the thymus. Another kind of thymic cancer derived from the medulla (the middle part of the thymus) is called medullary carcinoma. This is an uncommon type of cancer different in its appearance, behavior, and prognosis compared to other thymic cancers.
What Is Medullary Carcinoma of the Thymus?
One of the very interesting variants of epithelium neoplasms is medullary carcinoma of the thymus whose designation refers to the origin of this tumor, within the medulla of the thymus, which contains fewer lymphocytes or immune cells than the outer cortex. MCT is, in fact, histologically as distinct as other forms of cancer of the thymus, except for squamous cell carcinoma. These features make MCT a unique form of thymic cancer.
In the medullary region of the thymus, epithelial cells are closely packed and from which MCT arises. Such cancers are aggressive in nature because they are invasive in the tissues around the chest, and thus such cancers are hard to treat compared to other cancers of the thymus. This is a rare instance, so scanty work has been done in this area, and there hardly exist standard protocols for such treatment; often it proves to be challenging for doctors as well as patients.
How Does Medullary Carcinoma of the Thymus Present Clinically?
It is usually asymptomatic at its initial stage, and most symptoms that one undergoes are not specific, which makes early diagnosis of medullary carcinoma of the thymus quite rare. Most patients are found presenting with such symptoms as chest pain, chronic coughing, shortness of breath, or swelling of the veins of the neck and upper chest. These arise from local compression by the tumor upon adjacent intrathoracic structures, including the lungs, heart, or blood vessels.
Most patients with MCT have been diagnosed incidentally as part of an imaging study, such as X-rays or CT scans done for other reasons. MCT is unlikely to be associated with paraneoplastic syndromes compared with other thymic tumors, such as thymomas. Paraneoplastic syndromes are diseases that arise as a direct consequence of the immune system reaction caused by the tumor and can include myasthenia gravis, a disease involving muscle weakness. MCT is diagnosed when it has grown large or spread to the surrounding tissues, having its nonspecific symptoms.
What Is the Diagnostic Approach for Thymus Medullary Carcinoma?
The diagnosis of MCT is done by a combination of clinical examination, imaging studies, and tissue biopsy. Imaging studies, such as computed tomography and magnetic resonance imaging, provide the main modalities that describe the size, location, and the extent of the tumor. Secondly, CT scans help more clearly indicate structures infiltrated by tumors, like lungs, heart, or great vessels. If the imaging raises a suspicion that the tumor is present, then biopsy can prove it.
It would be a matter of taking small tissue portions from the tumor to be observed microscopically. Fine needle aspiration, wherein cells are extracted from the tumor with a thin needle, can be done. Surgical biopsy is often preferred, however if the tumor is in an inconvenient location. MCT can be diagnosed by a pathologist through the appearance of the tissue sample's cells. This is usually confirmed by a procedure known as immunohistochemistry, where special dyes are put to tissue that highlights proteins in cells. Some of the common proteins that may exist in MCT include cytokeratin, cluster of differentiation five (CD5), and cluster of differentiation 117 (CD 117).
How Is MCT Treated?
Treatment of medullary carcinoma of the thymus depends on the aggressiveness of the disease at the time of diagnosis. As MCT is such a rare tumor, there has been no protocol set up for the treatment. Physicians most often look to other types of cancers of the thymus as modalities in such a case.
The treatment depends on the stage of the tumor at the time of diagnosis:
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Surgery: Surgical excision is the only form of treatment for localized tumors, but a large proportion of patients cannot be fully resected due to site or size of the tumor.
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Radiotherapy: This modality is used as postoperative treatment in an attempt to control residual tumor growth and may be useful alone when complete surgical excision is not possible or prudent.
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Chemotherapy: It is used for advanced disease or with metastasis-the prognosis is grim. The drugs used are Cisplatin and Doxorubicin.
What Is the Prognosis for MCT?
The prognosis for medullary carcinoma of the thymus is multifactorial and depends on several factors, including the stage of cancer at the time of diagnosis, whether the tumor can be completely removed by surgery, and how well the patient responds to additional treatments such as radiation and chemotherapy. Unfortunately, MCT tends to have a worse prognosis compared with other thymic cancers.
Long-term survival following complete removal of the tumor varies from 30 percent to 50 percent, depending on the extent of the tumor. The prognosis in those with advanced or metastatic disease is, however, considerably poorer, with a median survival of less than two years. Recurrence is also very common, especially when total resection is not possible or if adjuvant therapies, like radiation or chemotherapy, have failed.
Conclusion
Thymic medullary carcinoma is a rarely encountered aggressive neoplasm with special diagnostical and therapeutic problems. Consequently, most often it is diagnosed at an advanced stage due to the vagueness of its symptoms, which can make treatment quite difficult. Surgery remains the cornerstone of any possible treatment, but radiation and chemotherapy are also commonplace in order to handle those cases that cannot be treated with surgery. The prognosis for MCT remains bad, especially for the patients in whom the disease has reached an advanced stage. Further studies are thus needed to develop better treatment options and improve overall results.
