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Female firefighters in San Francisco are facing their biggest battle yet — breast cancer.

The city by the bay has more female firefighters than any other city in the United States, but an increasing number of those women are being diagnosed with the disease.

The department says approximately 16 percent of its firefighters are women. Of that number, 15 percent of female firefighters between 40 and 50 years old have been diagnosed with breast cancer, which is six times the national average.

"Cancer is a concern for the San Francisco Fire Department as well as the fire service nationwide. But in San Francisco, we have seen and we do have numbers of elevated cancer rates for male and female firefighters," said Jeanine Nicholson, deputy chief of administration for the San Francisco Fire Department.

Over the last decade, more than 250 of the department's active and retired firefighters — both men and women — have died from various forms of cancer.