The diagnosis of a malignancy involves the following process
1. High clinical suspicion / Clinical probability ( based on the history of specific complaints/Age & Sex of the person/ethnicity/family history/life style related factors of the person etc)
2. screening tests ( usually simple, cost effective & non invasive tests )
3. Confirmatory tests (usually an invasive test like Biopsy
is there a definitive test to detect malignancy, which are non invasive..i must say no. Since all theses non invasive tests are not very sensitive ( Ability to detect a particular disease in question) or specific ( ability to rule out particular disease in question). That means some uncertainty will be there what ever may be the result of a screening test.
But if you can mention the specific malignancy about which you are concerned, we can answer you better