The endocrine system is a network of glands that produce and release hormones, which are chemical messengers controlling many bodily functions like metabolism, growth, mood, and reproduction. These glands include the pituitary, adrenal, parathyroid, and the thyroid. When cancer develops in any of these hormone-producing organs, it is classified as an endocrine malignancy. The most frequently diagnosed cancer originating in this system is thyroid cancer.
Thyroid Cancer Prevalence in the Endocrine System
The thyroid gland, a butterfly-shaped organ located at the base of the neck, is the most common site for endocrine system malignancy. This gland produces hormones that regulate heart rate, body temperature, and energy use. In the United States, thyroid cancer is estimated to be the 13th most commonly diagnosed cancer overall and the 6th most common among women, with an incidence rate in females sometimes nearly three times as high as in males.
Thyroid cancer is diagnosed in far greater numbers compared to other endocrine cancers. For example, in 2020, an estimated 586,000 cases were reported worldwide, making it the 10th most common cancer globally. The increasing number of diagnoses has been largely attributed to the more frequent use of advanced medical imaging, such as CT scans and ultrasounds, which can detect very small, often asymptomatic tumors.
While the incidence rate rose rapidly for several decades, largely due to the detection of these smaller tumors, this trend began to plateau and even decline slightly after 2014. The disease remains highly prevalent, especially in women and at a younger average age of diagnosis, around 51 years old, compared to most other adult cancers. The vast majority of these cancers are derived from the follicular cells, which produce thyroid hormone.
Categorizing Types of Thyroid Cancer
Thyroid cancer is not a single disease, but rather a group of malignancies with distinct cellular origins, behaviors, and prognoses. The four main types differ significantly in their severity and approach to treatment, with the vast majority falling into the differentiated category.
Papillary Carcinoma
Papillary carcinoma is the most frequently diagnosed form, accounting for approximately 80 to 90% of all thyroid cancers. This type typically grows slowly and often remains confined to the thyroid gland, making it highly treatable with an excellent prognosis. The cells look similar to normal thyroid cells under a microscope, reflecting their differentiated nature.
Follicular Carcinoma
Follicular carcinoma is the second most common type, making up about 4% of cases, and it also arises from the follicular cells. While still considered a differentiated cancer, it is slightly more aggressive than papillary carcinoma. Follicular cancer tends to spread through the bloodstream to distant sites like the lungs and bones, rather than primarily through the lymphatic system.
Medullary Thyroid Cancer (MTC)
Medullary thyroid cancer (MTC) is a rarer type, representing about 2% of all thyroid malignancies. This cancer originates from the parafollicular C cells, which produce the hormone calcitonin, not thyroid hormone. MTC can sometimes be hereditary, linked to a mutation in the RET proto-oncogene, and it does not typically respond to the same treatments as the follicular-cell derived cancers.
Anaplastic Carcinoma
Anaplastic carcinoma is the rarest and most aggressive form of thyroid cancer, making up only about 1% of cases. This undifferentiated cancer grows very rapidly and often invades surrounding structures in the neck. Its cells look highly abnormal under a microscope, and this type carries the poorest prognosis among all thyroid cancers.
Detection and Primary Treatment Methods
The process of diagnosing thyroid cancer often begins with the discovery of a thyroid nodule, an abnormal lump of cells within the gland. A physical examination may reveal a palpable mass, but many nodules are found incidentally during imaging tests performed for unrelated medical reasons. When a nodule is identified, the first step is typically a neck ultrasound to determine its size, number, and characteristics, such as whether it is solid or fluid-filled.
If the ultrasound reveals suspicious features, such as irregular margins or microcalcifications, the next step is a fine-needle aspiration (FNA) biopsy. During this procedure, a very thin needle is inserted into the nodule, guided by ultrasound, to collect a small sample of cells for microscopic examination. The FNA biopsy is the most definitive way to determine if a thyroid nodule is benign or malignant.
For most confirmed thyroid cancers, the primary intervention is surgery. The extent of the surgery depends on the size and type of the tumor and whether it has spread outside the gland. A total thyroidectomy involves the removal of the entire thyroid gland, while a lobectomy removes only the half of the gland containing the tumor. The decision between these two surgical approaches is guided by factors like the patient’s risk profile and the characteristics of the tumor.