An internal probe at a St. Cloud cancer center found that patients were given incorrect doses of radiation that could have resulted in their cancer returning or caused tissue damage.

The St. Cloud Times reports that CentraCare Health CEO Ken Holmen said a "small group" of cancer patients at the Coborn Cancer Center had been affected by treatment errors that resulted in them being over or underexposed to radiation from summer 2012 through last fall.

The newspaper says the consequences could include the recurrence of cancer, or burns and tissue damage that could potentially have contributed to death.

"We are extraordinarily sorry and regret that this occurred. We're committed to working with the patients and their families in whatever way they think best fits them," Holmen, who said staff have been disciplined or fired over the errors.

Holmen told the St. Cloud Times said that overexposure to cancer treatment radiation can cause tissue damage and is not enough to kill a person, but did say that the situation is "complicated by the fact that cancer patients don't have normal tissues to begin with."

The internal report, which was compiled after concerns were expressed by several employees at the center, is being investigated by the Minnesota Department of Health and a Minneapolis law firm, according to the Star Tribune.

The newspaper spoke with 79-year-old Betty Zollner, of Paynesville, who said she suffered partial paralysis when "misfired treatments" damaged a healthy part of her spine near the tumor for which she was being treated.

The newspaper notes that Zollner's case is one of three "mistakes" that are currently under investigation after being self-reported by the cancer center in the last year. It is not clear whether any others are under investigation as a result of the internal audit.