'Full House' star David Coulier announces stage 3 cancer diagnosis. What to know about non-Hodgkin lymphoma and the symptom that tipped the actor off.

Former Full House star Dave Coulier has been diagnosed with stage 3 non-Hodgkin lymphoma, a form of cancer that affects the lymphatic system, the actor announced on the Today show Wednesday. The 65-year-old actor said he had no symptoms until a cold left him with a golf ball-sized swelling in his groin. A visit to the doctor for the unusual lump ultimately led to Coulier’s cancer diagnosis. It was a “gut punch,” he told Today. Coulier is now undergoing treatment and says the prognosis is good — an outcome he credits to quick screening. Here’s what to know about Coulier’s diagnosis.

How Dave Coulier found out he had cancer

Just over a month ago, Coulier came down with a cold. He told Today he was accustomed in the past to swollen lymph nodes in his neck and armpits when he’d had mild illnesses. That’s a common occurrence when the body is ramping up immune cell production to fight off a cold. But in a matter of days, he developed a much more dramatic inflammation in a new spot, his groin. “It swelled up immediately,” Coulier told Today.

The enlarged node made Coulier think he might be sicker than he had realized, so he visited his doctor. PET and CT scans, an EKG and blood work all came back normal, but it was a biopsy — done as a precaution — that revealed that Coulier had cancer. “Hey, we wish we had better news, but you have non-Hodgkin lymphoma, B-cell lymphoma,” Coulier’s doctors told him. “The first thing I said to them was, ‘Wait a minute — cancer?’”

Coulier next had to have his bone marrow biopsied to find out whether the cancer had spread, which determines its stage. “That was pins and needles for a few days, because I didn’t know what stage it was, or if it had progressed,” he said. The results indicated that his non-Hodgkin lymphoma was at stage 3, meaning that the disease was present in multiple areas of the lymphatic system, but not in any other organs, according to the American Cancer Society (ACS).

Once his cancer was staged, doctors quickly scheduled Coulier for surgery to place a port through which he would receive chemotherapy. “You hear chemo, and it scares the daylights out of you,” he told Today. “The first round was pretty intense, because you don’t know what to expect.” Coulier has undergone at least one chemotherapy treatment, and will have six in all, spaced out every 21 days, and finishing in February. In total, Coulier said he’s undergone three surgeries in addition to chemotherapy, which has caused him to lose “a little bit of hair.” Because his cancer hasn’t spread beyond the lymphatic system, Coulier said his doctors estimate that there’s about a 90% chance his disease is curable, and that he is anticipating “total remission.”

What is non-Hodgkin lymphoma?

Non-Hodgkin lymphoma (sometimes simply called NHL) is a form of blood cancer that strikes the white blood cells of the infection-fighting lymphatic system. "NHL develops due to a mutation in one of the three lymphocyte cells," or immune cells, Christian Barnett, an information specialist with the Leukemia and Lymphoma Society, tells Yahoo Life. "The mutation changes the instructions for cell growth or reproduction, which causes the abnormal lymphocytes to grow out of control."

Non-Hodgkin and Hodgkin lymphoma are similar diseases, but they’re treated differently, according to the ACS. In both cases, cancer cells begin to multiply in the lymph nodes (interconnected, bean-sized repositories of immune cells located throughout the body, including in the chest, neck, abdomen and pelvis), in the immune cell-producing spleen or bone marrow or in the lymph tissue of the digestive tract or throat.

NHL accounts for about 4% of all cancers diagnosed in the U.S., and about 80,620 Americans are expected to be diagnosed in 2024, according to the ACS. On average, about 74% of people with NHL survive for at least five years, including between 71% and 77% of those diagnosed at stage 3, like Coulier. While Coulier is very optimistic about his prognosis, he is also making peace with uncertainty. He told his wife, “I don’t know why, but I [am] OK with whatever the news [is] going to be, no matter how devastating,” according to Today. But Coulier also said cancer is “a bit of a battle, and you’re going to need to be on your game.”

Chemotherapy is the first line of treatment against NHL. Depending on the stage, however, some patients also undergo radiation, immunotherapy, targeted therapy, surgery or stem cell transplants.

Know your risks and get screened

"The exact cause of NHL is not known, but there are risk factors that may increase the likelihood of developing the disease," says Barnett. "Some of these factors are immune disorders, medicines, infections, lifestyle, genetics, race, family history and occupational factors." As with many cancers, a family history of the disease and older age are risk factors for NHL, which usually strikes people between 65 and 74, according to the National Cancer Institute. It’s also more common among men and white people than among women or people of color. People with compromised immune systems due to conditions like rheumatoid arthritis or HIV are also at greater risk, and certain infections, including Epstein-Barr virus, may bump up someone’s odds of developing NHL. As with colorectal cancer, a high BMI may also further increase your risks, the ACS says.

Coulier’s main symptom — severely swollen lymph nodes — is a common first sign of NHL, Barnett says. "The most common early sign of NHL is painless swelling of one or more lymph nodes, but there are other signs and symptoms of NHL that are also associated with a number of other, less serious diseases." NHL symptoms include a fever with no obvious cause, night sweats, unexplained weight loss, fatigue, a rash or itchy skin and unexplained pain in the chest, abdomen or bones. Although these symptoms can usually be explained by something else, they’re worth getting checked out if they are persistent.

Getting his swollen lymph nodes examined may well have saved Coulier’s life, and he hopes his example will encourage others to do the same. “If I can help someone … get an early screening — a breast exam, a colonoscopy, a prostate exam — go do it, because, for me, early detection meant everything,” Coulier told Today.