MESA, Ariz. — Mesa firefighter Nikki Sullivan passed away Wednesday night after a five-year battle with breast cancer.

Her family believes she was exposed to toxins during her 15-year career with the department.

“She had genetic testing done that didn’t show any of the known genes that cause breast cancer. She doesn’t have any familial history," said her husband, Tim Sullivan. "Without a doubt, we feel that she either had an exposure or multiple exposures to the hundreds of thousands of chemicals we encounter.”

Since Sullivan's diagnosis in 2014, the Mesa Fire Department has implemented safety protocol to reduce toxicity, a department member said.

“Since Nikki’s diagnosis, there has been a lot of attention brought to what we are exposed to," said fellow firefighter Jenni Reeder.  “Making it aware of all the off-gassing and being able to clean ourselves right away and the department supporting us, staying out of service while we get showered.”

RELATED: An inside look at how Phoenix firefighters handle the risks of the job

The fire department is arranging funeral services. She leaves behind her husband, 6-year-old daughter, Abbi, and lots of friends.

The family has a Gofundme account set up in her name. You can also make a donation to cancer research in Nikki's name at this link.

RELATED: Phoenix firefighter dies of cancer contracted in the line of duty, firefighters association says