This study includes 297 patients who received operation at Kosin University Gospel Hospital from June 2008 to June 2010. The authors obtained patient medical records such as clinicopathologic factors and clinical data with serial levels of the serum CA15-3 during the follow-up period. This study employed the criteria that were used in Reporting Recommendations for Tumor Marker Prognostic Studies. Patients in the data set were categorized into 5 groups by the changing pattern of CA15-3 during the follow-up period. In group 1 (surge without decline), serum tumor marker increased continuously during the followup period. In group 2 (surge with incidental decline), incidental decline of serum tumor marker was followed by subsequent continuous surge. Patients in group 3 (decline without surge) showed continuous serum tumor marker decrease during the follow-up period. In group 4 (decline with incidental surge), incidental surge of the CA15-3 level was followed by subsequent continuous decline. Lastly, patients in group 5 (no changes) showed less than 10% change in the level of serum CA15-3. This study defines the surge of CA15-3 as an increment of CA15-3 by 10% or higher from preoperative baseline. When CA15-3 decreases by 10% or higher from the preoperative level, it is defined as the decline of CA15-3. To measure the TNM stage, this study used the criteria that were developed at the sixth American Joint Committee on Cancer. ER and PR positivities were defined as tumors with 1% or less of nuclear-stained cells. The first day of follow-up was considered as the day when pathological diagnosis was performed for the first time. Clinical follow-up was carried out every 6 or 12 months, which includes physical examination, laboratory tests of CA15-3, chest radiography, breast and liver ultrasonography, and bone scan. Five-year disease-free survival rate (5Y DFS) was measured as the time period from surgery to the occurrence of an event such as locoregional recurrence, distant metastasis, or death without recurrence. Locoregional recurrence was defined as pathologically confirmed relapse that is found on the chest wall, supra- and infraclavicular fossa, axillary area, or internal mammary region. Distant metastasis was confirmed by using radionuclear imaging modality, and pathology assessment if needed. This study was approved by the Kosin Medical Center Institutional Review Board.

The authors measured serum CA15-3 at the preoperative period as well as at follow-up. CA15-3 level was compared between preoperative baseline and the level at the 6 months follow-up. This study measured the difference of the level between the two points and changes were reported in percentage (i.e., less than 10% or 10% or greater). Serum CA15-3 levels were determined using an automatic electrochemistry luminescence immunoassay system (ROCHE E170; Roche, Mannheim, Germany). The cutoff value of CA15-3 level was the increment (or decrement) of 25 U/mL, and the value of tumor marker was measured by computing the deviation from the cutoff. Tumor marker has positive value if serum level is above the cutoff and negative value when serum level is below the cutoff. The kinetics of serum CA15-3 levels were computed from the slope of an exponential regression curve that connects the semilogarithmic values of CA15-3 (Ln CA15-3 = log CA15-3/log e). Microsoft Excel software 2007 (Microsoft Inc., Redmond, WA, USA) was used to calculate the equation of the curve: y = a.exp (px; p = slope of the curve; x = number of months between follow-up periods; a = the corresponding CA15-3 value). For the surge group, two CA15-3 slopes were calculated per patient using the initial elevated serum CA15-3 level, the peak level, and the decreased level during each period. The mean score of the two slopes was then obtained.

Survival curves were estimated by Kaplan-Meier method. Statistical tests were performed using IBM SPSS Statistics ver. 21.0 (IBM Co., Armonk, NY, USA). The survival function considered the time period from the onset of disease to the recurrence of disease. Survival data were censored out on December 31, 2014, which was the date when the survival data were correlated with the death registry for the last time or 5 years from the onset of the disease. Kaplan-Meier estimates are presented as the survival function. Log rank test was performed to test the significance of differences in survival rates. Associations between specific histopathological features and survival estimates and curves were established using the Kaplan-Meier method. The differences that were observed in survival functions among patient subgroups were tested by twosided log-rank test. All survival rates were presented with their standard errors. Pearson correlation was used to determine the association of pairs of explanatory variables. Differences in qualitative variables were evaluated by chi-square test, where necessary. All P-values were two-sided and a P-value of less than 0.05 was considered statistically significant.

Histopathological features such as hormone receptor status by immunohistochemical examination (Dako, Copenhagen, Denmark) were analyzed by the Institute of Pathology at the University of Kosin. Expressions of p53, estrogen receptor (ER), Ki-67, and human epidermal growth factor receptor 2 (HER2) were determined immunohistochemically on paraffin sections using antibodies against ER (Dako), Ki-67 (Dako), HER2 (Dako), and p53 (Dako). Histologic grading was performed using the criteria of Bloom and Richardson. Lymphatic vascular invasion was defined as the presence of tumor emboli in peritumoral lymphatic spaces, capillaries or postcapillary venules. ER status and PR status were taken as positive if more than 10% of tumor cells showed staining. HER2-positivity was indicated by a 2+ or 3+ score from the immunohistochemical examination, and the results were confirmed using a fluorescence in situ hybridization test for HER2. The cutoff point of 14% was used for Ki-67 staining. The molecular subtypes were classified into 4 groups; Luminal A (ER+ and/or PR+, HER2-, Ki-67<14%); Luminal B (ER+ and/or PR+, HER2+ and/or Ki-67 ≥14%); HER2 positive (ER- and PR-, HER2+); and triple-negative (ER- and PR-, HER2-). The classification follows the molecular subtype consensus of the St. Gallen International Expert Consensus on the Primary Therapy of Early Breast Cancer 2011.

The median value of serial serum CA15-3 samplings of each patient was 8.

The patients' clinicopathologic characteristics are described in Table 1. There were no significant differences among the 5 groups in terms of age, breast cancer subtype, method of surgery, American Joint Committee on Cancer (AJCC) stage, body mass index, adjuvant chemotherapy method and radiation therapy. No significant differences were found among the five groups in terms of adjuvant chemotherapeutic agents, adjuvant endocrine treatments, and anti–HER2-directed trastuzumab therapy.

The main clinicopathologic characteristics of the patients in our series are summarized in Table 1. Mean age was 50 years. T1 stage was reported for 88 patients (57.0%). N0 stage was reported for 153 patients (47.0%). All patients underwent surgery: conservative surgery was carried out for 93 patients (31.3%) and mastectomy was performed on 188 patients (63.3%). Radiotherapy was delivered to 148 patients (49.8%). Adjuvant chemotherapy was administered to 252 patients (84.8%): 152 patients (51.2%) received combination chemotherapy with cyclophosphamide, methotrexate, and fluorouracil; 66 patients (22.2%) received anthracycline-based therapy; and 34 patients (11.4%) received taxane-based therapy. Endocrine therapy was administered to 241 patients out of 297 patients (81.1%). Tissue HER2 status was positive for 40 patients (13.5%) and negative for 180 patients (60.6%). And the kinetics of serum CA15-3 were not significantly associated with the AJCC stage pathologically (Table 1).

Among 297 breast cancer patients whose serum tumor markers were serially collected during the follow-up periods, the number of patients in group 1 (surge without incidental decline) was 30 patients (10.1%), and 85 patients (28.6%) for group 2 (surge with incidental decline). Group 3 (decline with incidental surge), group 4 (decline without incidental surge), and group 5 (no change) were assigned 80 patients (26.9%), 73 patients (24.6%), and 29 patients (9.8%), respectively. 5Y DFS of the groups were 73.3% (group 1), 91.8% (group 2), 89% (group 3), 90% (group 4), and 100% (group 5) (P = 0.004) (Fig. 1, Table 2). The pairwise comparison with log rank test indicates that the 5Y DFS of group 1 is significantly different from other groups (P = 0.001, P = 0.012, P = 0.031, and P = 0.001, respectively). But no significant differences were found in the other pairs in the comparison (Table 3).