– The Chiba Cancer Center announced that a woman in her 30s had a breast removed unnecessarily after it mixed up test samples from two patients.

The woman had only early-stage cancer, and did not require immediate surgery.

The two samples were collected at the hospital on the same day in mid-October, one from the woman in her 30s and the other from a woman in her 50s. Both underwent needle biopsies, in which cellular tissue is collected by piercing the breast with a needle.

The mix-up resulted in the younger woman being told she had advanced cancer. The patient and her family agreed to surgery, and in early December a total mastectomy of the right breast was performed.

However, when the removed portion was examined on Dec. 15, only early stage cancer was found.

On Dec. 17, the hospital performed genetic tests on the two women, which revealed the mix-up. The older woman is receiving treatment.

The hospital was already undergoing reforms after it was revealed that 11 patients had died from 2008 to 2014 after undergoing laparoscopic surgery. The hospital is looking into compensating the woman in her 30s.