Thyroid cancer, while generally uncommon, includes several rare types. These less common forms account for a smaller percentage of all thyroid cancer diagnoses but often present unique characteristics and challenges. This article provides information on rare thyroid cancers, outlining their types, diagnosis, specialized treatments, and long-term care.
Types of Rare Thyroid Cancer
Medullary Thyroid Carcinoma (MTC) is a distinct rare type, making up about 2% to 5% of all thyroid cancers. Unlike common papillary and follicular types, MTC originates from parafollicular C-cells, which produce calcitonin. About 25% to 30% of MTC cases are hereditary, often linked to a RET proto-oncogene mutation, and can occur as part of Multiple Endocrine Neoplasia type 2 (MEN2) syndrome. The remaining cases are sporadic.
Anaplastic Thyroid Carcinoma (ATC) is among the most aggressive and rarest forms, accounting for less than 2% of all thyroid cancers. It is characterized by rapid, uncontrolled cell growth, often presenting as a quickly enlarging neck mass. ATC cells are highly abnormal and do not resemble normal thyroid cells, making them difficult to treat.
Thyroid Lymphoma is another rare cancer, comprising only 1% to 2% of thyroid malignancies. This cancer develops from lymphocytes within the thyroid gland. It is frequently associated with pre-existing Hashimoto’s thyroiditis, an autoimmune condition that increases the risk of developing thyroid lymphoma by 40 to 80 times.
Other rare types of thyroid cancer include thyroid sarcoma and metastatic cancers that spread to the thyroid from other parts of the body. Thyroid sarcomas are extremely rare tumors arising from the connective tissues of the thyroid. Metastatic cancers to the thyroid, such as those from kidney or breast cancer, are uncommon but can occur, often indicating advanced disease from the primary site.
Symptoms and Diagnostic Process
Symptoms of rare thyroid cancers can vary but often include a rapidly growing lump or swelling in the neck. Individuals might also experience voice changes, such as hoarseness, difficulty swallowing, or a persistent cough not related to a cold. Neck pain can also be a symptom.
The diagnostic process begins with a physical examination, where a healthcare provider feels the neck for lumps or changes in the thyroid gland and assesses nearby lymph nodes. A detailed medical history is also taken, including any family history of thyroid cancer or radiation exposure.
Imaging tests are a subsequent step, with neck ultrasound being the primary method to visualize the thyroid and any suspicious nodules. Ultrasound can reveal characteristics like calcium deposits or irregular borders, which may suggest cancer. Other imaging, such as CT, MRI, or PET scans, may be used to determine if the cancer has spread beyond the thyroid or neck.
A biopsy is performed to confirm a diagnosis, most commonly through a fine-needle aspiration (FNA). During an FNA, a thin needle is inserted into the thyroid nodule, often guided by ultrasound, to collect a cell sample for microscopic examination. This procedure determines if the cells are cancerous and the specific type of thyroid cancer.
Blood tests also play a role in diagnosis, particularly for suspected Medullary Thyroid Carcinoma. Specific markers, such as calcitonin and carcinoembryonic antigen (CEA), are measured; elevated levels can indicate MTC. Genetic testing is also important for MTC to identify inherited RET proto-oncogene mutations, which guide treatment decisions.
Specialized Treatment Modalities
Treatment for rare thyroid cancers is highly individualized, depending on the specific type and stage. Surgical removal of the thyroid gland, known as a total thyroidectomy, is often the primary treatment. This procedure aims to remove all cancerous tissue and may also involve removing nearby lymph nodes if cancer spread is suspected.
Radiation therapy is utilized, particularly for anaplastic thyroid carcinoma (ATC) and advanced medullary thyroid carcinoma (MTC), as these types do not absorb radioactive iodine. External beam radiation therapy delivers high-energy rays to destroy cancer cells or slow their growth. While effective for local control, radioactive iodine therapy, common for papillary and follicular thyroid cancers, is ineffective for rare types like ATC and MTC due to their inability to take up iodine.
Targeted therapy and immunotherapy represent modern approaches that attack cancer cells by targeting specific genetic mutations or by harnessing the body’s immune system. For instance, anaplastic thyroid cancers with BRAF gene mutations may respond to targeted drugs like dabrafenib and trametinib, which inhibit proteins involved in cancer growth. Immunotherapy, such as anti-PD-L1 inhibitors, can also be combined with targeted therapies to enhance the anti-tumor effect, especially in aggressive types like ATC.
Chemotherapy is another treatment option, particularly for anaplastic thyroid cancer, often used with external beam radiation therapy. Chemotherapy drugs destroy rapidly growing cancer cells throughout the body. While traditional chemotherapy may have limited effects on metastatic disease, it can be part of a multimodal strategy to manage aggressive rare thyroid cancers.
Prognosis and Long-Term Care
The prognosis for rare thyroid cancers varies significantly depending on the specific type, stage at diagnosis, and the cancer’s response to treatment. For example, localized medullary thyroid carcinoma generally has a better outlook compared to anaplastic thyroid carcinoma, known for its aggressive nature and rapid progression. Prognosis factors include tumor size, spread to lymph nodes or distant organs, and the patient’s age at diagnosis.
Following initial treatment, lifelong follow-up with a specialized medical team is important. This team often includes endocrinologists, surgeons, and oncologists who monitor for any signs of recurrence. Regular monitoring involves physical examinations of the neck and thyroid bed, along with imaging tests such as neck ultrasounds.
Blood tests are a routine part of long-term care to check for recurrence. For medullary thyroid carcinoma, calcitonin and CEA levels are continuously monitored, as rising levels can indicate disease recurrence. For other types, thyroglobulin levels may be checked, though this marker is not useful for anaplastic thyroid cancer or most medullary thyroid cancers. If recurrence is detected, further treatment, often involving surgery, radiation, or systemic therapies, is considered.