When Norwood, 65, began treatments in early December, he said he hoped to be at full strength when the new Congress convened Jan. 4.
Spokesman John Stone said aides have been encouraging the lawmaker to focus more on his health and not on work, particularly when his vote won't affect the outcome, as was the case this week.
Extended chemotherapy — complicated by fragile health from a 2004 lung transplant — has significantly weakened Norwood and left him spending some nights in a northern Virginia hospital.
The seven-term Republican from Georgia said he was not considering a leave of absence.
"What else would I do?" he joked in a phone interview earlier this week, shortly before President Bush's address on Iraq.
"I just gotta get through it," Norwood said of the chemotherapy regimen. "They think they can corral (the cancer). I just gotta get through it."
Norwood, a dentist from Augusta, missed votes this week on the Democrats' "100 hours" agenda, including votes on increasing the minimum wage and expanding federally funded embryonic stem-cell research.
His latest bout is believed to be a side effect of immune suppression drugs he takes as a result of his 2004 lung transplant. He suffers from idiopathic pulmonary fibrosis, a chronic lung disease that required the transplant.
Last year, doctors discovered a small cancerous tumor on his non-transplanted lung. They removed the cancer with surgery, but then discovered more cancer on his liver when Norwood returned to Washington after the November elections.