Background: Much research is being carried out to find a tumor marker for early diagnosis of breast cancer when the lesion is still small. CA15-3, a glycoprotein, is one candidate with probable use as tumor marker in breast cancer. Objective: We conducted this study to analyze the relationship between serum levels of CA15-3 and several variables including age, clinical stage, and the number of lymph nodes involved in breast cancer patients. Methods: One hundred and thirty-six females including 39 normal controls, 54 patients with benign lesions, and 43 with malignant lesions entered this study. A second and third sample was obtained from patients who were diagnosed as having breast cancer, one week and one month postmastectomy, respectively. CA15-3 was measured by ELISA. Results: The number of patients in the malignant group (6 out of 43) with elevated CA15-3 levels was higher than that in the normal controls (3 out of 39) and patients with benign lesions (1 out of 54). Forty percent of patients in stages II and III had a higher frequency of abnormal CA15-3 values, whereas 13 of those in stage I disease did so. One week after mastectomy, the mean ± SD serum CA15-3 was 18.3 ± 14.6 U/mL. However, a month later, the mean ± SD was 21.7±19.7 U/mL, which was approximately the same as the preoperative values (mean ± SD: 22.1 ± 25.6 U/mL). There was an abnormal elevation in CA15-3 values when �4 lymph nodes were involved. The correlation between the elevated CA15-3 values and the number of involved lymph nodes was significant (P < 0.001). Analysis of the CA15-3 values showed a sensitivity of 14.0 and a specificity of 92.3. The positive and negative predictive values were 66.7 and 49.3, respectively. The relative efficiency was 1.8. Conclusion: In this study, CA15-3 was found to have no value in the screening for early diagnosis of breast cancer. We observed a strong correlation between elevated CA15-3 levels and the progression of breast cancer
