JEFFERSON CITY, Mo. (AP) – Missouri Sen. Claire McCaskill says she’s returning to work after breast cancer treatment.

The Democratic senator told reporters Monday that she has received a good prognosis. She spent three weeks in St. Louis receiving treatment, including surgery to remove a lump and some surrounding tissue. McCaskill said the cancer was detected early through a regular mammogram.

McCaskill said the treatment provided “a really good time for me to refocus on some of the things that are really important in life.” She said she spent a lot of time with her husband and did a lot of reading.

McCaskill is backing former Secretary of State Hillary Clinton in Missouri’s Democratic presidential primary Tuesday.

McCaskill said the cancer treatment prevented her from actively campaigning on Clinton’s behalf.