Jimmy Carter's Cancer: How Doctors May Find Where It Started
Credit: Nir Levy / Shutterstock.com

Former President Jimmy Carter has not revealed much about his recent cancer diagnosis, but an important part of caring for anyone with cancer is finding out where the disease started, so that doctors can best treat it, experts say.

Yesterday, Carter released a statement saying that during a recent liver surgery, doctors discovered metastatic cancer. Metastatic means cancer that has spread to other parts of the body from where it started.

"I will be rearranging my schedule as necessary so I can undergo treatment by physicians at Emory Healthcare," Carter said.

The former president did not say if his doctors know where his cancer started, or how extensively the cancer had spread.

If doctors find metastatic cancer and don't know where it started, there are several things they can look for to determine the cancer's site of origin, said Dr. Moshim Kukar, an assistant professor of surgical oncology at Roswell Park Cancer Institute in Buffalo, New York, who has not treated Carter.

If doctors are able to take a biopsy of the tissue and look at it under a microscope, certain features of the cells can reveal where the cancer came from, Kukar said. Imaging of the site of a cancer can also inform doctor's understanding of the cancer's origin; for example, a tumor that starts in the liver looks very different on a scan than a tumor that has spread to the liver from the colon, Kukar said.

Doctors will also consider the organ in the body in which a metastatic growth is found, because "certain tumors have a predilection to go to one organ more than others," Kukar said. "Depending on where the spread is, you can figure out where it could have started."

For example, cancer that starts in the colon or other parts of the gastrointestinal tract commonly spreads to the liver, said Dr. Stephanie Bernik, chief of surgical oncology at Lenox Hill Hospital in New York City.

Doctors also take into account a patient's family history and his or her symptoms when trying to figure out a cancer's site of origin, Bernik said. "It's like putting the pieces of a puzzle together," Bernik said. In Carter's family, several people have had pancreatic cancer — three of his siblings had it, and his father died from the disease — so pancreatic cancer would be a concern in his case, Bernik said. [Why Is Pancreatic Cancer So Deadly?]

Finding out where a cancer started is very important because this information guides a patient's treatment, as well as helps determine the prognosis, Kukar said. Surgery is very rarely done for patients with metastatic cancer, but the choice of chemotherapy drugs and other treatments that may be done depend on where the cancer originated, Kukar said.

For example, colon cancer that spreads to the liver can be curable, so patients with this diagnosis would be treated very aggressively, Bernik said. On the other hand, pancreatic cancer that spreads to the liver is usually not curable, and so treatments are geared toward extending life in a meaningful way, Bernik said.

Carter said he will make a more complete public statement about his diagnosis at a later time, possibly next week, when more facts are known.

Follow Rachael Rettner @RachaelRettner. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.