Girl asks Santa for cure to her brother's cancer

ATLANTA -- A little girl is breaking hearts this Christmas thanks to her heartfelt plea to Santa Claus for the cure to her brother's cancer.

Kasie Muir Hart shared the letter her seven-year-old daughter Allie wrote to Santa Claus, which reads, "I want a cure for cancer because my 13-year-old brother has cancer. I have been really good this year, please try," wrote Allie.

Robert Hart was diagnosed with acute lymphoblastic leukemia in 2010 and has since been receiving treatment for it.

Muir Hart shared the letter to Facebook on December 12, writing, "Sweetest and saddest thing I've ever read. Now, if anyone can find the cure for childhood cancer in the next few weeks that would be swell if not a little girl is going to wonder why."