In addition, carcinoembryonic antigen (CEA) serum levels were associated with treatment response, since CEA decline correlated with a near complete radiological response and, conversely, elevated CEA serum levels were associated with progressive disease.
The CEA response was defined as CEA-complete response (CEA normalization), CEA-partial response (≥50% decrease in CEA levels), CEA-progressive disease (≥50% increase in CEA levels) and CEA-stable disease.
Secondarily, increasing CEA was able to identify all PD patients (sensitivity (Se) = 1.0) and in 50-74% of the patients increasing CEA provided a lead time to PD on upcoming CT.
Calcitonin levels >4,020 pg/mL (P = .0004), CEA levels >26.8 ng/mL (P = .04), and a calcitonin doubling time <24.1 months (P = .015) were associated with progressive disease in our cohort.