Durbin's office said surgeons removed the small tumor on Thursday. The surgery had been scheduled for several weeks, his office told NBC Chicago.
"This particular type of tumor is a rare form of stomach cancer, so it is cancer, yes," Durbin spokesman Joseph Shoemaker said, according to the Chicago Tribune.
A statement from Durbin's office said further treatment is not expected. It said the preliminary biopsy results "demonstrate a favorable prognosis."
The senator should be released from the hospital on Friday or Saturday and be able to resume a full schedule as early as next week.
Durbin, 65, is second to Majority Leader Harry Reid in the Senate Democratic leadership ranks.