What kind of blood test should be done for seminoma and malignancy?

HCG: This and PLAP (placental alkaline phosphatase) are often elevated in the presence of seminoma, but they are neither sensitive nor specific. There is no good blood test to search for cancer in general -- everything that's been tried ends up generating more morbidity from unnecessary procedures than the few lives saved are probably worth. Routine cancer screening is still the best appraoch.