The appendix is a part of the gastrointestinal system. It is a pouch-like structure that connects the small intestine with the large intestine, and it is located on the right side of the lower abdomen. The function of the appendix is not known, but it is believed to play a role in the immune system. Several types of cells are present in the appendix. These include epithelial cells, goblet cells, and hormone-producing cells.
Different types of cells in the appendix have a prespecified rate of division. However, due to genetic mutations, information related to the rate of division is either altered or deleted. These mutations may result in the uncontrolled division and growth of appendix cells, leading to the formation of tumors. This condition involving uncontrolled growth and division of appendix cells is called appendix or appendiceal cancer.
Appendix cancer is rare and affects about 1 to 2 people per million people. The condition is commonly diagnosed in people between the ages of 50 and 55. However, it may occur at any age. Further, there has been a reduction in the age of diagnosis during the recent decade. The condition is often diagnosed incidentally when the appendix is removed or the person undergoes an imaging evaluation for some other condition. The condition is usually diagnosed late; almost one-third of the cases are diagnosed after metastases.
Appendix carcinoma can arise from different appendix cells, and it is classified into different types based on the type of cell from which it arises. Following are the different appendix cancer types:
It is a type of neuroendocrine tumor, and the most common type of appendix cancer. These tumors account for almost 50% of all appendix tumors. These tumors are relatively more common in women than in men. If diagnosed at an early stage, carcinoid tumors have a favorable prognosis. The initiation of carcinoid tumors of the appendix occurs in the hormone-producing cells.
Adenocarcinoma of the appendix initiates in the lining of the appendix. The different types of appendiceal adenocarcinoma include:
It is the second most common type of appendiceal cancer, the first being carcinoid tumors. The cancer starts in the appendix lining and produces a jelly-like substance known as mucin. Mucin may assist in the spread of mucinous adenocarcinoma to other body parts. The condition is often diagnosed after metastasis to the abdominal cavity lining. The severity of these tumors is graded based on the involvement of mucosa, i.e., mucinous adenoma, low-grade appendiceal mucinous neoplasms, and high-grade mucinous adenocarcinoma.
Colonic-type adenocarcinoma is also known as intestinal-type adenocarcinoma. These tumors account for 10% of all the appendix tumors. This cancer type often starts at the appendix base. These are similar to colorectal tumors and are presented with various similar symptoms.
These are aggressive types of epithelial tumors. Almost 60% of signet ring cell adenocarcinoma cases are diagnosed after they are metastasized to distant sites. These are rare tumors. When these cells are viewed under the microscope, they have a look-alike signet ring inside them. These cells store and secrete a large amount of mucin.
It is a rare type of tumor of the appendix. It is often diagnosed incidentally while routinely managing acute appendicitis. The condition is less aggressive than adenocarcinomas but more aggressive than conventional appendiceal cancers. It is usually diagnosed in people in their 50s and 60s and has a similar incidence in men and women. Patients with this condition experience abdominal pain and the presence of abdominal mass.
It is a rare tumor characterized by changes in the epithelium of the appendix. Patients with mucinous cystadenoma have a marked distension in the lumen of the appendix with mucin. The symptoms are similar to those of acute appendicitis. The condition is usually diagnosed incidentally during surgery or imaging. Approximately 25% of the patients with mucinous cystadenoma are asymptomatic.
Paraganglioma of the appendix is rare. The condition may occur anywhere in the GI tract, but predominantly in the duodenum. These are usually considered benign but may potentially invade the lymph nodes and distant organs.
The TNM classification is used to determine the severity or extent of appendix cancer. Determination of the stage of appendiceal cancer may help in developing treatment strategies and predicting the prognosis. The TNM classification suggests the size of the tumor (T), its invasion of the lymph nodes (N), and the spread of the tumor to other organs (metastasis, M).
This stage is known as carcinoma-in situ. The cancerous tumor in the appendix is localized, i.e., the tumor is confined to the appendix and has not spread outside.
Stage 1 appendix tumor invades the inner layer of the appendix but does not spread to the lymph nodes or distant organs.
Stage 2A appendiceal cancer spreads to the fatty or connective tissue of the appendix. Stage 2B appendiceal cancer invades the lining of the appendix. Stage 2C appendiceal cancer spreads to nearby organs, such as the rectum or colon. The cancer does not invade lymph nodes or other body parts.
Stage 3A appendiceal cancer invades the inner appendix layers and 1–3 surrounding lymph nodes. Stage 3B appendiceal cancer invades the nearby appendix tissue or appendix lining and 1–3 nearby lymph nodes. Stage 3C appendiceal cancer invades ≥ 4 lymph nodes. However, the cancer has not invaded other body parts.
Stage 4A appendiceal cancer spreads to abdominal cavity organs and may or may not spread to regional lymph nodes. Stage 4B appendiceal cancer invades abdominal organs and lymph nodes, but the cells are poorly differentiated. Stage 4C appendiceal cancer reaches distant organs, such as the lungs.
Appendix cancer initiates in the appendix. The different appendix cancer types include carcinoid tumor (the most common appendix cancer), appendiceal adenocarcinoma, mucinous adenocarcinoma, colonic-type adenocarcinoma, signet-ring cell adenocarcinoma, goblet cell carcinoid tumor, and paraganglioma. Stage four appendix cancer is the most advanced stage of appendiceal cancer.