Jeff Bridges, the acclaimed actor who became a cult icon with his role in “The Big Lebowski,” shocked his legions of fans when he announced Monday he has been diagnosed with lymphoma, a type of blood cancer.

Bridges, 70, said his prognosis was “good,” adding that he was starting treatment. But he did not specify whether he had been diagnosed with Hodgkin lymphoma or non-Hodgkin lymphoma, the two main subtypes of lymphoma.

Hodgkin lymphoma is typically treated with a chemotherapy regimen known as ABVD. Non-Hodgkin lymphoma is also typically treated with chemotherapy drugs, but the exact regimen depends on the cancer subtype.

In contrast to non-Hodgkin Lymphoma, Hodgkin lymphoma tends to spread to neighboring lymph nodes first before eventually makes its way to the rest of the body if untreated. In other words, a lymphoma that arises in the neck will first spread to the lymph nodes near the collarbone, with subsequent spread to the arm and the chest.

In both cases, lymphoma strikes the tissues and organs that produce, store and carry white blood cells that fight infections, according to the Centers for Disease Control and Prevention. The lymphatic system, otherwise known as the body’s germ-fighting network, includes the lymph nodes, spleen, thymus gland and bone marrow, according to the Mayo Clinic.

The National Cancer Institute estimates that there will be 8,480 new cases of Hodgkin lymphoma in 2020 and 77,240 new cases of non-Hodgkin lymphoma over the same period. The latter figure represents roughly 4.3 percent of all new cancer cases this year, according to the institute’s statistics.

The rates of Hodgkin lymphoma are highest among teenagers and young adults (ages 15 to 39), and again among older adults (ages 75 or older); non-Hodgkin Lymphoma is most common as people get older.

The symptoms for lymphoma include enlarged lymph nodes — typically in the neck, armpit or groin — as well as fatigue, shortness of breath, unintentional weight loss and night sweats, according to the CDC.

Bridges, beloved for his laid-back personality and gentle disposition, struck an optimistic tone in a pair of tweets Monday.

He announced his diagnosis by paraphrasing a line from “The Big Lebowski” (“New S**T has come to light”), adding that he felt fortunate for having his team of doctors, and for the love of his family and friends.

“Thank you for your prayers and well wishes. And, while I have you, please remember to go vote. Because we are all in this together,” Bridges said in his second tweet, directing his Twitter followers to a voter information and registration website.

The actor received an outpouring of support on social media: “Star Trek” actor George Takei, crime novelist Don Winslow and political journalist Jonathan Alter were among those who tweeted well-wishes to the actor.

The comedian Travon Free tweeted: “Hey 2020, leave Jeff Bridges out of this!”

Bridges, who made his film debut in the early 1970s, has been nominated for seven Academy Awards. He finally won an Oscar in 2010 for his performance as a grizzled alcoholic country crooner in “Crazy Heart.”

But he is most widely known for his turn as the Dude — a floppy-haired pothead who chugs White Russians and loafs around Los Angeles — in the Coen brothers’ cult classic “The Big Lebowski.” The movie failed to light up the box office in 1998, but it eventually developed a devoted following on DVD.

The actor’s other notable films include “Thunderbolt and Lightfoot,” “Starman,” “The Fabulous Baker Boys,” “The Fisher King,” “The Contender” and the first installment in the “Iron Man” series.

Bridges hails from a family of show business veterans. He is the son of the actor Lloyd Bridges and the actress Dorothy Bridges, and the younger brother of the Emmy-winning actor Beau Bridges, his co-star in “Bakers Boys.”

He was recently filming “The Old Man,” a television series slated to debut on Hulu via the FX cable network.

“Our thoughts go out to Jeff and his family during this challenging time, and they have our love and support,” FX, Touchstone Television, Hulu and FXP said in a joint statement posted online. “We wish him a safe and full recovery.

“And, as Jeff always says, ‘We are all in this together.’ Jeff, we are all in this together with you.”