Aleisha Hunter's wide smile and carefree energy give no hint that the four-year-old recently endured a 15-month-long medical nightmare that ended with a diagnosis of breast cancer and a full mastectomy.

Aleisha, from Cambridge, Ont., is thought to be Canada's youngest breast cancer survivor, having endured an illness that would terrify any grown woman, but one that the preschooler still doesn't quite understand.

Aleisha's mother, Melanie, still doesn't quite understand it either.

She says the first time she noticed the pea-sized lump on Aleisha's chest was in December, 2008, when Aleisha was two and a half. She took her daughter to her doctor, who said it must be a bacterial infection of her lymph nodes, a condition called lymphatic inflammation.

"They basically didn't know what it was and I wasn't satisfied with their answer and she was getting sicker," Melanie told CTV News. "She had quite a bit of pain. Most of her pain was at night, she stopped sleeping."

When the lump started to grow in January, 2010, Melanie became even more worried. It grew to 2.5 centimetres by April and by the time surgeons went in to remove it, the lump had grown to five centimetres, was turning purple and spreading out like a web.

Doctors diagnosed Aleisha with secretory breast carcinoma, a rare type of invasive breast cancer in which the tumour secretes fluid. Because cases of it are so rare, little research has been done on this type of cancer. But what is known is that it's a relatively non-aggressive form of cancer that doesn't spread quickly, and most patients recover well with treatment.

Dr. Nancy Down, a surgical oncologist at North York General Hospital, helped perform a radical modified mastectomy on Aleisha, which meant removing the entire breast along with the lymph nodes under the arm.

"Cases like Aleisha's are so rare you can almost count them on one hand," Dr. Down says. "We've looked through the literature & the youngest we've found is three."

The two-hour surgery was a success, and Aleisha's mother, Melanie, says once her daughter got home, the difference was even more remarkable.

"She's much happier. She's feeling much better. She's bouncy. She's growing. She's putting on weight," Melanie reports.

Now, Aleisha is getting used to living a life that other four-year-olds take for granted. Melanie says her daughter is getting through her health scare by asking lots of questions.

"She's a survivor. She understands that she's had cancer and the doctors fixed her," she says.

But for Melanie herself, it will take longer to get over the trauma.

"It was very scary at first when we got the diagnosis," she says. "My support was basically my co-workers and friends. I didn't really have time to seek outside help."

Dr. Down says Aleisha's prognosis is good and when she's older, she may choose to do reconstructive surgery.

"The likelihood is that she will live a very long life," she says.