Bone-oma's

I find it difficult to remember the differences between osteoblastoma, osteoid osteoma, chondrosarcoma, and osteosarcoma. So here's how I remember:

• If it begins OSTEO and ends OMA then it happens at a young age (generally <40 years)
• If it begins CHONDRO then it's over 40's (so I think of John-drosarcoma and John Lennon being shot aged 40)

 And here are the amusing ways to remember which one is which: