Parathyroid Cancer (Carcinoma of the Parathyroid Gland)
What is parathyroid cancer?
Parathyroid cancer (carcinoma) is a malignant tumor of the parathyroid gland. It is a rare type of cancer that originates from the uncontrolled growth of the cells of the parathyroid gland. Since the cancer starts in the parathyroid cells itself, it is also known as a primary cancer. If cancer that starts elsewhere in the body and spreads to the parathyroid gland, then it is known as a secondary cancer or metastatic cancer. Parathyroid carcinoma is one of the rare cancers. It affects about 1 in 7.5million people and affects both males and females equally. Most cases of parathyroid cancer are seen in people over the age of 30 years.
Malignancy of the Parathyroid Gland
Parathyroid gland and functions
The parathyroid gland is not a single structure but rather a collection of four small glands. There are two small glands on the right and two on the left of the the back of the thyroid gland. The upper glands lies towards the top of the thyroid gland within the neck but the lower glands can dip into the upper part of the mediastinum, the central compartment of the chest cavity. The parathyroid grands produce and secrete parathyroid hormone (PTH). The main function of parathyroid hormone is to regulate the calcium and phosphate levels in the body. Most of the calcium and phosphate are stored with the bones.
- Parathyroid hormone increases the release of calcium and phosphate from the bone and into the blood.
- Parathyroid hormone decreases loss of calcium and phosphate through the urine by increasing its reabsorption from the kidneys.
- Parathyroid hormone increases the absorption of calcium and phosphate in the gut in conjunction with vitamin D.
Cancerous tumor
Cancer of the parathyroid gland is not significantly different from cancer in other parts of the body. Normally cells in the body replicate when it is severely worn out, damaged or when it reaches the end of its lifespan. Programmed cell death is known as apoptosis. Replication ensures that cells that die are replaced by new and healthy cells. In cancer the process of cell replication and cell death becomes disordered usually due to some damage to the DNA of the cell. The cells replicate rapidly and these new cells are often abnormal. Furthermore these cancerous cells do not die due to apoptosis and continues to multiply, often invading surrounding healthy tissue. If these cancerous cells break away from the site, it can spread through the bloodstream or lymphatics to cause cancers elsewhere in the body (metastatic cancer).
Effects of parathyroid cancer
Most cancers of the parathyroid gland are functional tumors meaning that it increases the production and secretion of parathyroid hormone. Only a minority of these cancers are non-functional. It is also important to know that most parathyroid tumors which cause overproduction of parathyroid hormone are benign (non-cancerous) and not malignant (cancerous). Therefore parathyroid cancer is in most instances marked by an excess of parathyroid hormone, a condition known as hyperparathyroidism. In very rare cases, the spread of the cancerous parathyroid cells to other parts of the body can cause tumors outside of the parathyroid gland which then produces parathyroid hormone. Due to the normal function of parathyroid hormone, an excess will lead to weakening of the bone, formation of calcium and phospate stones in the kidneys and elevated blood calcium levels (hypercalcemia).
Signs and Symptoms
There are the generalized symptoms of cancer that may also be seen in parathyroid carcinoma. This includes weight loss, fatigue and changes in appetite. More specific symptoms of parathyroid cancer are largely due to hypercalcemia. Therefore non-functional cancers of the parathyroid gland may be largely asymptomatic until late stages of the disease.
- Constipation
- Excessive thirst
- Frequent urination
- Bone pain
- Abdominal pain
- Muscle and joint pain
- Muscle weakness
- Nausea and vomiting
- Fatigue
- Frequent fractures
- Fatigue
- Loss of appetite
All of these symptoms are non-specific for parathyroid cancer and there are various other more common diseases that are more likely to lead to these symptoms.
Causes of Parathyroid Cancer
The causes of parathyroid cancer are not largely different from the causes and risks of other types of cancer. It is largely due to genetic mutations and defects that impair normal cell growth and death. However, the exact cause in the majority of cases still remains unknown. Although different genes have been identified as a possible cause of parathyroid cancer, there are two conditions which are strongly associated with this type of cancer – hyperparathyroidism-jaw tumor syndrome and multiple endocrine neoplasia (MEN I).
Hyperparathyroidism-Jaw Tumor Syndrome
Defects in the CDC73 gene affects the production of a protein known as parafibromin. This protein is believed to play a role in the proliferation of cells. It causes uncontrolled cell proliferation and the formation of tumors. These tumors cause hyperparathyroidism and about 15% are cancerous. The defect in the CDC73 gene may be inherited and is an autosomal dominant trait meaning that only one copy of the gene from a parent is a sufficient to lead to this condition.
Mutiple Endocrine Neoplasia (MEN) I
Multiple endocrine neoplasia type I is a condition where certain glands become overactive and may develop tumors due to genetic defects that can be inherited. The mutations of the MEN1 gene, which codes for the menin protein, can involve any gland but more commonly affects the parathyroid, pituitary or pancreas glands. Sometimes only a single gland is affected while at other times multiple glands are involved at the same time.
Tests and Diagnosis
Various tests need to be conducted to confirm a diagnosis of parathyroid cancer.
- Blood tests for calcium and parathyroid hormone (PTH) levels may indicate hypercalcemia and hyperparathyroidism. However, parathyroid cancer only accounts for a minority of these cases.
- Further investigation with imaging studies are therefore necessary. An x-ray may be the first indicator of an abnormal growth. This prompts the need for surgical intervention. A computed tomography (CT) scan and positron emission tomography (PET) scan may help in evaluating metastatic spread of the cancer as as well as the stage of the malignancy.
- A biopsy is usually not done as it may increase the risk of the cancer spreading. Instead the tumor should be surgically removed and then the tissue examined under a microscope.
Parathyroid Cancer Medication
The cancer in the parathyroid gland cannot be treated with medication. Instead drug therapy is used for hypercalcemia (elevated blood calcium levels) – a common complication of parathyroid cancer. Hypercalcemia in parathyroid cancer is usually very severe and needs medical therapy in order to minimize any further complications.
- Calcitonin, a natural hormone, may be administered to help with regulating calcium levels.
- Gallium nitrate is used to lower the calcium levels.
- Bisphosphonates that are used in osteoporosis treatment are prescribed to limit further bone breakdown.
Paraythyroid Cancer Surgery
Minimally invasive surgery is often conducted to remove the tumor because of the severity of hypercalcemia without always identifying whether it is a benign or malignant tumor prior to surgery. It involves removing the entire tumor along with any normal gland tissue to which the tumor adheres. It is uncommon for there to be spread to lymph nodes around the parathyroid gland. If there is lymph node involvement, these nodes are then removed surgically.
Recurrence
The recurrence of parathyroid cancer is quite common. Chemotherapy and radiation therapy does not usually prevent recurrence of the cancer although it may limit spread. Instead repeat surgery is indicated if the cancer recurs. Over 60% of patients with parathyroid cancer may have a recurrence of the malignancy, sometimes as delayed as 20 years or more later.
Survival Rate
The 5 year survival rate in parathyroid cancer is between 50% to 70%. Death from parathyroid cancer is quite common. It can sometimes be due to untreated hypercalcemia rather than the cancer itself. There are various reasons why death is common in this type of cancer. A delayed diagnosis and poor medical care are some of the factors that may contribute to mortality.
References :
http://www.nlm.nih.gov/medlineplus/ency/article/007264.htm
