Since achieving pCR is related to better survival outcomes (event-free survival [HR = 0.40, P < 0.001] and overall survival [HR = 0.32, P < 0.001]) in the NAC setting, it has been regarded as a dependable predictor [6]. Hence, the prediction of pCR in the early pre-treatment period is of great significance. However, the predictive biomarkers in other literature are not accessible to every patient for economic reasons or cumbersome steps. To fill this research gap and achieve the maximum utilization of resources, this study selected simple and easy-to-access core biopsy and clinical information of patients as predictive factors and built a prediction model for pCR in the NAC setting. It helps to predict chemotherapy response at the time of diagnosis and makes it possible for clinicians to intervene early in some high-risk patients. The selection of variables and the conditions of the model development are described in the ensuing paragraphs.
Clinical tumor staging
Clinical tumor staging plays a crucial role in chemotherapy response. Livingston-Rosanoff et al. reported a retrospective study that included 38,864 patients who underwent NAC treatment and subsequent surgery for a solitary lesion varying from cT1 to cT3, which revealed that cT3 tumors have a lower probability of achieving pCR irrespective of molecular subtypes [20], which is consistent with our study. The possible explanation for this finding is that larger tumors have a higher chance of revealing heterogeneity of elevation, which may affect the sensitivity of chemotherapy [21]. Many prediction models involved clinical tumor staging (tumor size) as a predictive factor [22–24], which indicates it is a reliable factor for predicting pCR.
Clinical nodal status
In the last decade, the administration of systemic treatment in patients with node-positive disease has switched from the adjuvant to the neoadjuvant setting. According to previous studies, 20–42% of the firstly node-positive patients finally achieve pCR of the axillary lymph nodes [25]. Our results showed that pre-treatment clinical nodal status was associated with chemotherapy response; in other words, there was a greater possibility of pCR in patients with clinically node-negative disease, which is consistent with the previous study [26]. It reported the low probability of pathologic nodal positivity in patients with clinical node-negative and breast pCR disease [26], highlighting the crucial role of clinically node-negative in achieving pCR. Meanwhile, it indicated that clinical assessment by clinical diagnostic imaging played a vital role in pCR prediction. An accurate clinical assessment technique for recognizing patients with node-negative disease would be beneficial for BC care. Some models incorporated pre-treatment lymph node status for predicting axillary pCR for node-positive BC [27, 28], indicating the vital role of nodal status in pCR prediction.
ER status
ER, a vital factor that defines tumor subtype, has extensively been identified as a feature that affects the response to NAC [29]. Previous studies reported that ER-negative subtypes such as HER2-enriched and triple-negative BC were more likely to achieve pCR and favorable long-term outcomes [29, 30], which is consistent with our results. By analyzing pre-treatment ER as a continuous variable, we could divide patients into ER-positive and ER-negative or ER-high and ER-low diseases. Further, we found the cut-off value of pre-treatment status rather than simply dividing it into ER-positive and ER-negative, which could be explained by the fact that ER-low disease and ER-negative disease have similar biological behavior. Weisman et al. [31] found that ER-low malignancies had a semblable pathologic response to NAC treatment as ER-negative diseases, demonstrating the above point. It will separate the ER-positive patients into different subgroups with different probabilities of achieving pCR. Nevertheless, the cut-off value remains controversial. Few previous studies assessed ER status quantitatively, one of which reported a cut-off value of 30% when distinctions in responses could be seen among patients with ER < 30% and those with ER > 30% diseases [32], which is consistent with our results showing that the cut-off value of ER was 22.5%. Also, previous literature reported that the threshold of 80% best predicted the relation to pCR [33].
Ki67 status
Ki-67 is a biomarker of cell proliferation used to evaluate the invasiveness of the tumor; except for the G0 phase, the expression of Ki67 exists in all the cell cycle phases [34]. Ki-67 has been assessed in several studies for its predictive role in the NAC setting, but its cut-off value of it remains controversial. However, a large-scale meta-analysis incorporated 44 studies reported that pre-treatment high-Ki-67 was related to elevated pCR rates in BC patients who received NAC using distinct cut-off values of Ki-67 [35]. Our study found a threshold of Ki-67 was 32.5%, which is in the range from 15–50%, as previous literature reported [35].
p53 status
p53 protein, coded by the TP53 gene, the most frequently mutated gene in BC, plays a crucial role in metabolism, apoptosis, DNA repair, and cellular sensitivity to chemotherapy [36]. Numerous BC patients who will accept NAC treatment have cancers harboring TP53 mutations. Many studies have tried to identify the role of that mutation in pathological response, which showed that compared with wild-type counterparts, tumors with TP53 mutations have a statistically higher probability of pCR in BC [14, 37]. Replaced by simply dividing p53 status into positive and negative, the cut-off of 37.5% best predicted the correlation with pCR in our cohort, and patients with p53 ≥ 37.5% were more likely to have a pCR. Limited studies reported the threshold value of p53 in BC; Lee et al. [38] found that a threshold of 10% for p53 was a predictive factor of survival outcome. However, there were no studies on the cut-off value of p53 in the NAC setting. To our knowledge, this is the first study to explore the role of pre-treatment p53 in the NAC prediction model; moreover, the cut-off predictive value of p53 was found.
Prediction model
In summary, in our study, the model for predicting pCR had five variables, cT, cN, ER status, Ki67 status, and p53 status, respectively. Notably, we visualize the prediction model and present it as a nomogram. The ROC analysis and Hosmer-Lemeshow goodness-of-fit test indicated that the model had good discrimination and calibration; AUC = 0.804 (95% CI: 0.756–0.853; P < 0.001), sensitivity, and specificity of 73.2% and 74.7%, respectively, Hosmer-Lemeshow goodness-of-fit test χ2 = 7.089, P = 0.527 > 0.05. In clinical application, the probability of pCR can be judged by the total score obtained by adding the scores of each risk factor. For all we know, this is the first pCR prediction model that includes the expression level of pre-treatment p53 status. The optimal model is the model with the maximum net benefit for any given probability threshold. The DCA shows that outcome prediction using the model with p53 has a greater net benefit than the model without p53.
Limitation
The major limitation of this study is that the prediction model was developed based on the Chinese population and may not apply to other ethnic groups. Additionally, internal validation was conducted in the single data set because of the limited sample size, and no external validation group was established to validate this model. It is hoped that external validation will be conducted in further studies by conducting multicenter studies.