Breast cancer includes multiple molecular subtypes and is a highly heterogeneous solid tumor[20]. Neoadjuvant therapy has been proven to increase the radical resection rate and breast preservation rate. The treatment efficacy varies from person to person, and the clinical response is a method of early evaluation[21, 22].In this paper, we emphatically analyzed the viability of the RCB model and its influence on the prognosis after NAC. Our cohort was a collection of high-risk cases (Table 1: TNBC 18.9% and HER2-positive 20.9%), and the distribution of these subtypes was similar to that in the RCB validation groups performed by Symmans et al.[14, 16]. Although the research has some shortcomings, we found that the survival prediction of RCB was similar to that in previous studies.
The Miller-Payne grading system is an accepted model that compares preoperative and postoperative tumor tissues, and is extensively used in neoadjuvant efficacy evaluation in domestic hospitals[23]. According to the percentage of cell density reduction in primary tumor foci, the system categorizes NAT efficacy from class 1 to class 5[24]. Although it concisely and visually depicts the critical parameters associated with breast carcinomas and guides the selection of subsequent clinical treatment, it does not meticulously assess the postoperative pathology, particularly in patients with lymph node metastasis. And the MP system is not sufficiently comprehensive to measure the curative effect of tumor treatment due to the evaluation of only primary breast lesions. Moreover, following effective neoadjuvant therapy for smaller tumors, the decrease in tumor cell density is more obvious than that in larger tumors, which indicates that the change in tumor cell density alone is not sufficiently comprehensive and objective to evaluate the therapeutic effect of tumor treatment[25]. In contrast, the RCB system has more meticulous requirements for specimen collection and microscopic evaluation after neoadjuvant therapy. The RCB score contains information on the tumor foci and positive lymph nodes. The long and short diameters of the tumor foci, number of positive lymph nodes, proportion of the primary tumor beds that contain infiltrating cells and maximum diameter of the axillary lymph node metastasis are used to calculate the score after the NAC treatment [26]. And this system has been gradually recognized in China over the years.
As an effective postoperative pathological response evaluation system, RCB has been validated in many Western countries and regions. A classic clinical test (protocol MDACC-LAB98–240), with the longest cohort follow-up time of 13 years, revealed no difference in survival between low RCB grades; in contrast, poor prognosis was mainly associated with the higher RCB class, which was assessed by Symmans et al.[16]. This conclusion was validated in another study by Müller, H. D et al. ,who enrolled 184 cases[15]. In our retrospective study, we found that patients classified as RCB I (HR of RCB I vs. RCB 0=2.714, p=0.327) could have a good prognosis and a low risk of recurrence since these patients achieved pCR. As expected, patients with a higher RCB class had worse survival outcomes, as confirmed by the Cox multivariate analysis, where RCB II (HR of RCB II vs. RCB 0=8.695, p=0.006) and RCB III (HR of RCB III vs. RCB 0=14.330,p=0.001) were significant factors. The results are consistent with those obtained by others. Ki-67 represents cell proliferation and is a recognized risk factor in breast cancer patients[27, 28]. Our study show that patients had a shorter RFS with Ki67 >20%, which suggest that lesions with high proliferative capacity may have worse outcomes. The results are also consistent with findings in other studies[29, 30].
Young age is a known risk factor for long-term survival in patients who undergo breast-conserving surgery and are not treated with NAC[31, 32]. This view was verified by a meta-analysis of large-scale prospective tests of breast-conserving surgery, which suggested that younger female patients had a higher 10-year locoregional recurrence rate(LRR)[33]. Nevertheless, once the patients were treated with NAC, we could not able to assess the role of age in predicting survival outcomes. A large and authoritative EORTC 10994/BIG 1–00 study showed that younger age was not a risk factor for local recurrence(LR)[34], and another study by Müller, H. D et al. from Europe did not separately analyze the age[15]. Another study included 263 cases, with a cutoff value of 50 years, and mainly analyzed the impact of younger age on LR after NAC. The results revealed that patients <50 years could have higher pCR rates, and young age could have a better outcome after NAC[35]. Our study divided the cases by age into two sets, with 102 patients (40.2%)>50 years, and we concluded that older age (>50 years) would have a higher rate of relapse; however, we have no evidence to verify that younger age was highly predictive of pCR.
Our binary logistic regression analysis reveal that the phenotypic subtype was the unique associated factor in models that included age, stage, and chemotherapy regimens, and we found that patients with HER2-positive breast cancer, particularly TNBC, had higher pCR rates than HR-positive/HER2-negative patients. Similar conclusions have been observed in other studies[36, 37]. Increased RFS with pCR occurred regardless of the clinicopathological characteristics, including HR-positive/HER2-negative patients[38]. Finally, ROC curves were used to evaluate the prognostic efficiency of the RCB and Miller-Payne scoring systems for RFS, including calculation of the AUC, which demoNATrated the favorable diagnostic efficiencies of the RCB and Miller-Payne scoring systems, with AUCs of 0.711 and 0.682, respectively. Taken together, these data suggest that the two systems are promising predictors for breast cancer patients treated with NAC.
Some disadvantages remain in our study. The leading is that we had a short follow-up time for these patients and were unable to obtain the overall survival data. In the future, we will continue to expand the number of case samples and increase the follow-up time to obtain more convincing survival data. Second, our study may have introduced selection bias because the data came from only two hospitals. Last, due to the diversity of neoadjuvant chemotherapy regimens, 86.6% of cases had received the same kind of chemotherapy regimen.
Although the RCB system has more detailed requirements for evaluation, it can only be used to evaluate postoperative pathology. The cell density of thick-needle aspiration specimens before neoadjuvant therapy and surgical specimens after neoadjuvant therapy can’t be compared as in the Miller-Payne system and can’t reflect the contrast gap before and after neoadjuvant therapy, so it also has some limitations. Sheri et al. combined RCB score with the Ki-67 to form a "residual proliferative tumor load" (residual proliferative cancer burden, RPCB) system, and the RPCB score provided richer prognostic information and had a higher predictive efficiency[39]. Recent studies have combined tumor infiltrating lymphocytes (TILs) with the RCB score as an original evaluation system, particularly in TNBC, which also shows good prospects[40, 41].
Our team analyzed the differentially expressed genes of the resected tissue following NAT, and it is believed that promising biomarkers with prognostic value will be found soon. In addition, Shandong Cancer Hospital took the lead in performing internal breast lymph node biopsy in China[42-44]. We also envision combining the internal breast lymph node information with the RCB system to develop a new, more comprehensive and accurate postoperative pathological evaluation system.