AICR... Is this a scam?????

I received a letter in the mail from, AICR. It says they are cancer research, and trying to raise money for research. Oh and AICR stands for, American Institute for Cancer Research. I read what they sent, and decided to send some money. I only sent 25 dollars. I spoke to my boyfriend about it a few days later, adn he expressed to me that this was probably a scam, and I should not have mailed any money. I admit I did not research this letter. Now I fell like I should have. Did I get fooled? Is this a scam? It really looked legit. Please let me know if this is a scam. Should I cancel My check???