Negative CEA values in metastatic colorectal carcinoma and the likelihood of complete chemotherapy response

Experimental results reported in the literature have suggested that CEA might inhibit host defense mechanisms and that immunotolerance to CEA could play an important role in the development of metastases in colorectal carcinoma. It might therefore be assumed that negative CEA values during metastatic disease represent a favorable prognostic factor. Surprisingly, there are very few data available about negative CEA. The aim of this study was to determine the significance of negative initial CEA values in patients with metastatic colorectal carcinoma.

Initial CEA values were determined in 114 patients with metastatic colorectal carcinoma. The patients were divided into three groups according to these values: I (n=22) <5 ng/mL; II (n=33) 5-100 ng/mL; III (n=59) >100 ng/mL.

Seven/114 complete responses (CR), 22/114 partial responses (PR), 45/114 instances of stable disease (SD) and 38/114 of progressive disease (PD) were registered, while two patients were not evaluable. There were six long-lasting CRs (median 24 months, range 10-37 months) in the CEA-negative patient subset, while in the CEA-positive subset there was only one CR, in a patient with an initial CEA level of 18 ng/mL. The mean initial CEA values in the different response categories were: CR: 4.0 ng/mL; PR: 436 ng/mL; SD: 1442 ng/mL; PD: 6071 ng/mL. The likelihood of response, in particular CR, was highly dependent upon CEA levels (Fisher's exact test, 0.00001). The median survival decreased significantly with increased values of CEA (p=0.006).

Negative CEA in metastatic disease was the main characteristic of the patient subset capable of attaining CR. When relapsing, all patients but one became CEA positive.