My 15 yr old had an ultrsound & blood work and now the pediatrician wants her to see a obgyn oncologist at a children hospital. is he thinking cancer?

he may be: Oncologists are specialists in diagnosis and treatment of cancer. So if your doctor suspects cancer, he may ask an oncologists to investigate and guide him/her further and rule out cancer as a possibility.

Possibly: Without knowing the results of the tests, I am guessing about your daughter. The ultrasound would allow the ovaries to be visualized. The blood tests would possibly look for hormone markers (alpha-fetoprotein and beta human Chorionic Gonadotropin that would be potential tumor markers for an ovarian germ cell tumor. Possibilities include ovarian cysts, and benign and malignant ovarian tumors.