A carcinoid is described as a small tumor, usually found in the gastrointestinal tract, that secretes serotonin.

Serotonin is eventually metabolized by the liver, and excreted by the kidneys. A carcinoid sometimes secretes large amounts of serotonin into the blood, which can cause various forms of the carcinoid syndrome of flushing, diarrhea, and heart problems.

According to medical history, carcinoids were first characterized in 1907 by Siegfried Oberndorfer, a German pathologist at the University of Munich, who coined the term karzinoide, or "carcinoma-like", to describe the unique feature of behaving like a benign tumor despite having a malignant appearance microscopically.

According to the online source Wikipedia, most carcinoids are asymptomatic through the natural lifetime and are discovered only upon surgery for unrelated reasons. This is what took place for Matt Bynon, who entered the hospital for appendix surgery.

A carcinoid, specificially, is considered a hybrid between an exocrine and endocrine tumor derived from crypt cells of the appendix. The condition results in the formation of clusters of goblet cells with a distinctive growth pattern. They are sometimes called coincidental carcinoids. But all carcinoids are considered to have malignant potential.

About 10% of carcinoids secrete excessive levels of a range of hormones such as serotonin.

This can result in flushing, diarrhea, wheezing, abdominal cramping and peripheral edema.

The outflow of serotonin can cause a depletion of tryptophan leading to niacin deficiency. (Niacin deficiency, called pellagra, is sometimes associated with conditions such as dermatitis and even dementia.)

The most common originating sites of carcinoid is the small bowel. Carcinoid tumors are the most common malignancy of the appendix, although they have been known to be associated with the ovary or thymus.

Medical experts say surgery is the only curative therapy. If the tumor has metastasized (most commonly, to the liver) and considered incurable, there are some promising treatments for arresting the growth of the tumors and prolonging survival in patients with liver metastases, though they are currently in experimental stages.

Although opinions vary, some online sources say chemotherapy is of little benefit and is generally not indicated.

According to Wikipedia, "While the metastatic potential of a coincidental carcinoid is probably low, the current recommendation is for follow up in 3 months with CT or MRI, labs for tumor markers like serotonin, and a history and physical, and then annual physicals thereafter."

While carcinoid tumors are considered the most common malignant tumor of the appendix, "they are most commonly associated with the small intestine, and they can also be found in the rectum and stomach. They are known to grow in the liver, but experts say such a condition is usually a manifestation of metastatic disease from a primary carcinoid occurring elsewhere in the body. They have a very slow growth rate compared to most malignant tumors."

Goblet cell carcinoid, specificially, is considered a hybrid between an exocrine and endocrine tumor derived from crypt cells of the appendix. The condition results in the formation of clusters of goblet cells with a distinctive growth pattern.