The woman had at first received the news she'd hoped for following an initial mammogram: there was no tumor, the local Arbetarbladet newspaper reported.
But subsequent tissue samples gave a different answer.
According to that test, the 32-year-old was suffering from breast cancer, and the decision was taken to remove her breast.
After the operation, however, no tumor could be found.
The woman's unwarranted breast removal is the second such case to take place at the hospital in Gävle in recent months.
The Local reported in July about a 47-year-old woman who had her breast removed after a contaminated test led doctors to believe she had cancer.
Another woman, 34, had her breast removed by mistake following a misdiagnosis.
Johan Ahlgren of the hospital's oncology department said at the time that the mistakes were the result of a dearth of pathologists at the hospital.
“We've had a few too few pathologists during the past year, which has led to some mistakes. How many that could be I can't really say,” he told the local Gefle Dagblad newspaper in July.
The case of the 32-year-old has been reported to the National Board of Health and Welfare (Socialstyrelsen), and chief of medicine at the diagnostics department in the Gävleborg County Council, Bengt Larsson, expressed his regret about the incident.
“This is very unfortunate, it is not acceptable that things like this happen,” he told local newspaper Arbetarbladet.
“The stressful environment and the pressure to handle many tests may have affected what happened.”