Bob Dole, who served the state of Kansas for more than two decades, announced he has been diagnosed with cancer.
About 40% of all lung cancer diagnoses fall into the Stage 4 bracket, according to the Cancer Treatment Centers of America.
"While I certainly have some hurdles ahead, I also know that I join millions of Americans who face significant health challenges of their own", wrote Dole.
In 1997, Clinton awarded Dole the Presidential Medal of Freedom and, in 2018, Congress awarded him the Congressional Gold Medal.
In a tweet, Democratic Kansas Gov. Laura Kelly wished Dole "a swift recovery".
Dole lost the White House race to Democrat Bill Clinton, 20 years after losing the 1976 election as Gerald Ford's running mate, making him the only person to lose both the presidential and vice presidential elections on a major party ticket.
Dole's involvement in presidential politics is as lengthy as anyone to never hold the office.
Dole was elected to the Senate in 1968 and won re-election four times before resigning in 1996 to run for president.
Dole served with distinction in the Army during World War II, suffering serious injuries in battle in Italy.
He served with Clinton following the September 11, 2001, terrorist attacks as co-chairman of a scholarship fund for the families of the victims.
He led Republicans when they were in the minority for eight years, from 1987 to 1995, and then again as majority leader starting in 1995.