False Negative: Erroneous diagnostic finding that something is not true when it actually is true. Example: A patient with a low serum PSA level (below 4 ng/mL.) is thought to be free of cancer, but actually has cancer (false-negative PSA).
False Positive: Errorneous diagnostic finding that something is true when it actually is not true: Example: A patient with a high PSA (above 4 ng./mL) is thought to have cancer, but actually does not have cancer (false-positive PSA).
Flow Cytometry: Diagnostic test to determine DNA content of cancer cells.
Frequency: The need to urinate often.
Frozen section: Diagnosic test for intraoperative evaluation of tissue to determine the presence or extent of cancer. The pathologist snap-freezes the tissue, cuts it into thin slices, and examines it under the microscope, providing the results to the surgeon to modify the operation as appropriate.