WASHINGTON, DC - JULY 25:  Sen. John McCain (R-AZ) walks to the U.S. Senate chamber July 25, 2017 in Washington, DC. McCain was recently diagnosed with brain cancer but returned on the day the Senate is holding a key procedural vote on U.S. President Donald Trump's effort to repeal and replace the Affordable Care Act.  (Photo by Mark Wilson/Getty Images)
PHOTO: Mark Wilson/Getty Images North America/Getty Images
WASHINGTON, DC - JULY 25: Sen. John McCain (R-AZ) walks to the U.S. Senate chamber July 25, 2017 in Washington, DC. McCain was recently diagnosed with brain cancer but returned on the day the Senate is holding a key procedural vote on U.S. President Donald Trump's effort to repeal and replace the Affordable Care Act. (Photo by Mark Wilson/Getty Images)
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WASHINGTON, DC - SEPTEMBER 1: Cindy McCain looks on as a joint military service casket team carries the casket of the late Senator John McCain following his funeral service at the Washington National Cathedral, September 1, 2018 in Washington, DC. Former presidents Barack Obama and George W. Bush delivered eulogies for McCain in front of the 2,500 invited guests. McCain will be buried on Sunday at the U.S. Naval Academy Cemetery. (Photo by Drew Angerer/Getty Images)
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WASHINGTON, DC - SEPTEMBER 1: Cindy McCain looks on as a joint military service casket team carries the casket of the late Senator John McCain following his funeral service at the Washington National Cathedral, September 1, 2018 in Washington, DC. Former presidents Barack Obama and George W. Bush delivered eulogies for McCain in front of the 2,500 invited guests. McCain will be buried on Sunday at the U.S. Naval Academy Cemetery. (Photo by Drew Angerer/Getty Images)
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Secretary of Defense James N. Mattis and Chairman of the Joint Chiefs of Staff Marine Gen. Joseph F. Dunford Jr. will brief the media on Tuesday, Aug. 28, at 10 a.m. EDT, in the Pentagon Briefing Room (2E973).  DAILY SCHEDULE: Secretary of Defense James N. Mattis and Chairman of the Joint Chiefs of Staff Marine Gen. Joseph F. Dunford Jr. brief the media at 10 a.m. EDT in the Pentagon Briefing Room (2E973). Both U.S. and foreign journalists without a Pentagon building pass must be pre-registered in the new Pentagon Visitor Management System to attend this briefing; plan on being escorted from the River Entrance Pedestrian Bridge or the Pentagon Metro Entrance Facility only. Please arrive no later than 45 minutes before the briefing; have proof of affiliation and photo identification. Please call 703-697-5131 for any questions and escort into the building. The briefing will also be streamed live on www.defense.gov/live.  Secretary of Defense James N. Mattis hosts an enhanced honor cordon welcoming Minister of Defense Ryamizard Ryacudu of Indonesia, to the Pentagon at 2:30 p.m. EDT on the steps of the River Entrance. All journalists desiring to cover the cordon must obtain a wristband from security screening. Journalists without a Pentagon facility access card must go through security screening at the base of the River Entrance Pedestrian Bridge, and will be escorted to the cordon from there. Security screening will begin at approximately 1:45 p.m. EDT; have proof of affiliation and two forms of photo identification. Journalists with a Pentagon facility access card, and whom have entered the building prior to 1:30 p.m. EDT, may go through security screening at the River Entrance to obtain their wristband. All journalists wishing to cover the honor cordon, including those with a Pentagon facility access card, must be in place no later than 2:15 p.m. EDT. Once security screening has been initiated at the base of the bridge, all journalists entering the building via the bridge for any reason, including those with a Pen
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Story highlights

Sen. Thad Cochran has had health problems that kept him out of office this fall

Sen. John McCain is fighting brain cancer, a diagnosis he announced this summer

(CNN) —  

Republican leaders in the Senate are keeping a close eye on the health conditions of two senior members – John McCain of Arizona and Thad Cochran of Mississippi – ahead of a crucial vote on the GOP tax plan next week.

Both have missed votes this week, though party leaders expect the two senators to be in position to vote for the tax bill, which could happen as early as Monday.

McCain, who announced he had brain cancer this summer, was hospitalized this week “for normal side effects of his ongoing cancer therapy,” his office said in a statement Wednesday night.

“Senator McCain looks forward to returning to work as soon as possible,” the statement said, though it did not include any details on the timing of his return.

Cochran had “an outpatient procedure Monday afternoon to address a non-Melanoma lesion on his nose,” his spokesman Chris Gallegos told CNN. “The procedure was more extensive than expected, but the senator is doing well and available now for votes if needed.”

“Senator Cochran is in Washington and expects to vote for the tax plan when it comes to the Senate next week,” Gallegos added.

Sens. John McCain of Arizona (left) and Sen. Thad Cochran of Mississippi (right), both Republicans
PHOTO: Getty Images
Sens. John McCain of Arizona (left) and Sen. Thad Cochran of Mississippi (right), both Republicans

Cochran has had health issues throughout the fall, including a urinary tract infection that kept him out of office for several weeks in October. At the time, Cochran said he thought he was physically fit for office.

Republicans hold a slim majority in the chamber – 52-48 – and losing three votes would block their plans to overhaul the US tax system.

GOP Sen. Bob Corker of Tennessee voted against the Senate bill when it initially passed the chamber, though he has not said whether he’ll vote against final passage of the bill hammered out between the House and Senate.

RELATED: Key details revealed in Republican tax deal

Republicans have a very tight deadline to pass tax reform next week, with a long and pressing list of year-end actions they are planning to complete before leaving town for the holiday.