Entertainment Sports Marcus Smart Encouraging Donors to 'Get Out There and Help' After Losing Mom and Brother to Cancer Smart, a star point guard with the Boston Celtics, says losing his mom and brother "puts some fire in your heart" to get people to sign up to be stem cell donors By Megan Johnson Published on September 19, 2022 09:32 AM Share Tweet Pin Email Marcus Smart and his mother Camellia. Photo: Courtesy of Aflac Marcus Smart knows the pain of losing family members to cancer. That's why the Boston Celtics point guard is making it his mission to change the system. Smart, 28, has teamed up with Be the Match and Aflac to raise awareness about the need for more diverse donors on the Be The Match Registry, the world's largest listing of potential marrow donors and donated cord blood units. While 75 types of diseases can be treated with a blood stem cell transplant, only 29% of patients that are Black or African-American will find a match, since people are more likely to match with someone of the same race or ethnicity. It's a stark disparity compared to white patients, who have a 79% chance. "The discrepancy in the registry is beyond ridiculous," Smart tells PEOPLE. "We need people to join the registry and to become donors, because transplant is the only way. We're coming together and allowing what I've experienced in my life and what they've been doing to merge together and do something special." Celtics' Marcus Smart Will Donate Blood for Experimental COVID-19 Treatment After Recovering The mission to diversify the registry comes from a place of significant meaning for the Celtics star, who lost both his brother and mother to cancer. His older brother Todd passed away from lung cancer, and Smart saw the effects his disease had on his family. He watched his brother's weight drop, and his body slowly deteriorated. "But through all that, he was still smiling. He was this positive guy," said Smart, who was raised in Lancaster, Texas. "It put things in perspective for me in my life as I got older." Marcus Smart and Justice Brooks. Courtesy of Aflac And in 2018, Smart lost his mother, Camellia, to bone marrow cancer. The self-proclaimed "mama's boy" says his mother was "by far, my biggest fan and my biggest critic." "We had this thing where for every free throw I missed, I owed her $100. Long season, a couple missed free throws, that adds up!" he laughs. The struggle his family has dealt with has also served as tremendous inspiration for Smart. Jason Momoa Calls for Donors to the Be The Match Registry Inspired by Friend's Cancer "As the youngest of 4 boys, it puts some fire in your heart to get out there and help with the cause," he shared. On Tuesday, Smart welcomed 19-year-old Justice Brooks, who is living with sickle cell anemia, to his Massachusetts home. Brooks knows just how hard it is to find a match on the donor registry. At age 17, he made the decision to go through a blood stem cell transplant, even though the only match they could find on the registry was a 7/8 match. Marcus Smart and Justice Brooks. Courtesy of Aflac He then began his induction chemo to prepare for his transplant, but he contracted a bad lung infection that halted the plans. Now healthy once again, the Atlanta teen is on the hunt for a full 10/10 match. It's an important message for September, which is both Childhood Cancer Awareness Month and National Sickle Cell Awareness Month. "I want people to know what people with these diseases go through and how difficult it is," Brooks told PEOPLE. "And how they could help save somebody's life." On Tuesday, Brooks spent the day with Smart, chatting about video games and hanging out. "He's a real down-to-earth person," Brooks said of Smart. "We began talking about video games like I already knew him. He's easy, he's great." Aflac When he's not on the court, Smart enjoys everything from chess and bowling to tennis and playing board games with his girlfriend. "I just like to have fun," says Smart. "We struggle so much, everybody. Everybody has something going on, that sometimes we just need to laugh. And for me, I try to be positive and bring life."