A brother is credited with helping to save his little sister's life during a tickle fight in early July.

The Huffington Post UK reported that 11-year-old Aaron East from Essex, England, was tickling his 7-year-old sister Amy East when he noticed a lump on her neck.

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“I was really guilty at first because I didn’t understand much of what I found," Aaron told The Huffington Post UK. "I didn’t know what to do at first but then I realized I needed to let a responsible adult know so I ran to (my mommy) and I’m happy I did."

Aaron's discovery led doctors to diagnose Amy with rhabdomyosarcoma, a rare cancer that affects fewer than 60 children in the UK, early.

Amy underwent surgery to remove part of the growth and is now undergoing chemotherapy.

According to the family's GoFundMe page, Amy is set to undergo proton beam therapy, a form of radiotherapy that is only available in the United States. They are raising money to cover the cost of the trip and short- and long-term financial costs.