Tumor Marker Tracking Calculator

Serial tumor marker measurements -- PSA after prostatectomy, CEA in colorectal cancer follow-up, CA-125 in ovarian cancer surveillance, and similar assays -- are tracked over time because the trend usually carries more clinical meaning than any single value. This calculator converts two measurements and the days between them into a doubling time (assuming exponential kinetics, the same math used for PSA doubling time calculations in urology), a velocity in raw units per month, and a percent rate of change. The number of days recorded between the two draws has the largest effect on the calculated doubling time of any single input, because doubling time scales directly with that interval for a given pair of marker values -- the same rise measured over 180 days implies roughly twice the doubling time of an identical rise measured over 90 days -- so an approximated or mis-recorded date range can move the estimate as much as a real change in the marker values would. The projection window and the upper normal limit have no effect on the doubling time itself -- they only determine, respectively, how far forward the same measured rate is extrapolated and how the current value compares to a lab's reference range.

PSA doubling time under roughly three months (90 days) while rising is a commonly cited threshold in the urology literature for aggressive kinetics warranting closer follow-up or treatment reconsideration, which this calculator flags automatically -- but that 90-day cutoff is a PSA-specific convention, and this tool applies it regardless of which marker you actually entered, since it has no marker-type selector and no verified equivalent thresholds for CEA, CA-125, CA 19-9, or AFP. Treat the aggressive-kinetics flag as meaningful for PSA and only illustrative for other markers. PSA velocity thresholds such as 0.75 ng/mL per YEAR, referenced in this tool's velocity output, come from older PSA-based biopsy trigger literature and have been de-emphasized in more recent guidelines that favor other risk factors -- and note the units: this calculator's velocity output is per MONTH, so it must be multiplied by roughly 12 before comparing against that per-year threshold. This calculator assumes clean exponential growth between exactly two points; it does not smooth over assay variability between different labs or test kits, and marker fluctuations from causes other than tumor burden (inflammation, other benign conditions, assay noise) are not distinguished from true disease-driven change.