SAN DIEGO (FOX 5/KUSI) — A National City boy's brave fight against testicular Rhabdomyosarcoma, a rare and aggressive form of cancer, comes after a shocking diagnosis that turned his family’s world upside down.  Alex Balbin, 10, has stopped attending school in person due to his weakened immune system caused by chemotherapy treatment, which he recently started. His teacher and classmates have written him letters filled with words of encouragement as he navigates his health. Doctors removed a five-pound testicular tumor in late October and since then, the boy said he "feels more free." For six months before his surgery, Alex’s mother, Vee Balbin, said her son kept the mass growing inside his body a secret until it led to the emergency room. She explained that her son never had any pain and hid the tumor under oversized sweatshirts. The child's family knows getting through the next year of chemotherapy will be challenging, but they feel the support.  "I'm grateful for my friends and my friends' parents who’ve helped a lot," said his sister Nina Balbin. They hope to make a difference in the lives of others by sharing the lessons they’re learning. "Be aware. Ask your doctor if you notice anything, any changes in your kid. I wish I would've," said Alex's mother Vee Balbin. The family has set up a GoFundMe to help pay for Alex’s medical expenses and to ensure he has the support necessary to recover.