The Role of CA 125 as Tumor Marker: Biochemical and Clinical Aspects

CA 125 also known as mucin 16 or MUC16 is a large membrane glycoprotein belonging to the wide mucin family, encoded by the homonymous MUC16 gene. Following its discovery in the blood of some patients with specific types of cancers or other benign conditions, CA125 has found application as a tumor marker of ovarian cancer. Thirty years after its discovery, use of CA 125 is still FDA-recommended to monitor response to therapy in patients with epithelial ovarian cancer and to detect residual or recurrent disease in patients who have undergone first-line therapy and would be considered for second-look procedures. However, due to its limited specificity and sensitivity, CA 125 alone cannot still be an ideal biomarker. Increased clinical performance, in terms of better sensitivity and specificity in identifying epithelial ovarian cancer relapse, has been obtained by combined use of CA 125 with HE4, another ovarian cancer marker recently introduced in clinical use. Significant advancements have been achieved more recently, due to the introduction of FDA-approved ROMA and OVA1 algorithms to evaluate the risk of ovarian cancer for patients with a pelvic mass.

Early detection of recurrent ovarian cancer in patients with low-level increases in serum CA-125 levels by 2-[F-18]fluoro-2-deoxy-D-glucose-positron emission tomography/computed tomography

PURPOSE

Serum CA-125 has been shown to be a sensitive tumor marker of recurrent ovarian cancer. The goal of this study was to evaluate the use of 2-[F-18]fluoro-2-deoxy-d-glucose-positron emission tomography/computed tomography (FDG-PET/CT) in the early detection of recurrent ovarian cancer in patients with low-level increases in serum CA-125 levels.

METHODS

Patients who demonstrated a normalization of serum CA-125 levels after complete remission of ovarian cancer were recruited for this study. FDG-PET/CT was performed to evaluate serum CA-125 levels ≥ 35 U/mL (Group 1) or progressive low-level increases in the levels of serum CA-125 (Group 2). The results were analyzed based on pathology, disease progression, and/or clinical follow-up.

RESULTS

Twenty-seven (27) consecutive patients consented to the aforementioned criteria (n = 16 in Group 1 and n = 11 in Group 2). In Group 1, of the 16 patients, 15 had a proven tumor recurrence, and the remaining 1 had a second primary cancer with no evidence of recurrent ovarian lesions. In Group 2, all 11 patients had recurrent tumors. The use of FDG-PET/CT allowed the detection of recurrences in 25 patients and a second primary cancer in 1 patient, which included all of the patients in Group 1 and 10 of the 11 patients in Group 2. The detection rate of FDG-PET/CT for recurrent ovarian cancer was 100% in Group 1 and 90.9% in Group 2 (15/15 vs. 10/11, p = 0.423). FDG-PET/CT changed the intended management in 14 (53.8%) of the patients, which included 4 cases in Group 1 and 10 cases in Group 2.

CONCLUSIONS

FDG-PET/CT has the ability to detect recurrent ovarian cancer and second primary tumors in patients with increased levels of serum CA-125. FDG-PET/CT affects the clinical management by localizing recurrent lesions and creating a specific treatment plan for each patient, especially patients who demonstrate a low-level increase in serum CA-125 levels.

An Early Signal of CA-125 Progression for Ovarian Cancer Patients Receiving Maintenance Treatment After Complete Clinical Response to Primary Therapy

Purpose

For ovarian cancer patients receiving maintenance treatment after complete clinical response to primary therapy, we tested the predictive value of the following early signal of progressive disease (EPD) criterion based on serum CA-125: for patients with CA-125 nadir ≤ 10 U/mL, a confirmed value of ≥ 20 U/mL serves as an early signal of CA-125 progression; for patients with nadir more than 10 U/mL, a value ≥ 2× nadir that is confirmed predicts progression.

Patients and Methods

The EPD criterion was tested on Southwest Oncology Group trial 9701/Gynecologic Oncology Group trial 178 patients (n = 288) and compared with Gynecologic Cancer Intergroup criterion.

Results

For 204 patients with known progressive disease, the progression date was predated by EPD by ≤ 60 days in 31%, 61 to 180 days in 15%, and more than 180 days in 10% (median, 56 days early). Of 84 progression-free patients, nine EPDs were found. Overall, 135 patients met the EPD criterion. True disease progression status was undeterminable for two patients and nine were potentially false signals, for a conservative positive predictive value of 93% (95% CI, 88% to 97%).

Conclusion

Initial testing of the proposed CA-125 criterion resulted in a low false-positive rate and early prediction of disease progression in more than 50% of the patients tested. The proposed criterion may better reflect the timing of disease progression and should be investigated further.