Camejo, 67, said doctors found the cancer after he underwent an MRI last month for a swollen spleen.
"I was very lucky because it created pain and swelled my spleen," Camejo said in a telephone interview from his home in Folsom, a Sacramento suburb. "They are going to do several more procedures on me, and then I'll have a better idea of what my treatment will be."
Camejo said doctors believe his cancer is in the early stages and is treatable.
Lymphoma is a cancer of the lymphatic system and can occur most places in the body. The two main types of lymphoma are Hodgkin's disease and non-Hodgkin's lymphoma.
Some doctors believe the cancer can be caused by chemical exposure, a factor Camejo said he isn't ruling out.
"We have 200 chemicals in our body that we didn't have 100 years ago," Camejo said. "So many millions of Americans get cancer and to have to deal with it; it is a humbling experience."
As a gubernatorial candidate in California, he has supported abortion rights, universal health care and a moratorium on the death penalty. He ran for governor in 2002, 2003 and 2006. He also ran for president as the Socialist Workers Party nominee in 1976.
During the 2004 presidential contest, Camejo was independent Ralph Nader's running mate. Camejo is chair of the board of directors of Progressive Asset Management Inc., a broker-dealer firm he co-founded Oakland. He also is a board member of Earth Share.