In this study, we constructed a nomogram based on various imaging diagnostics and clinical indicators to predict the status of axillary lymph nodes after NAT. We identified 6 pretreatment factors as independent predictors of axillary pCR namely molecular subtypes, MG breast, CT breast, US axilla, MRI axilla, and CT axilla. Analyses in the training and the validation cohorts showed that the nomogram could predict the axillary pCR after NAT. In addition, the calibration curve demonstrated that the predictive model had satisfactory calibration. Collectively, our results show that the novel constructed nomogram is a reliable and relatively objective nomogram with good clinical utility that could facilitate the pretreatment prediction of axillary pCR after NAT.
The molecular subtype is an important index to predict the primary treatment focus for breast cancer patients after NAT. Further, molecular subtypes of axillary lymph nodes are also considered to be an important index and hence it is meaningful to be enrolled as a predictive factor in the nomogram model. In this study, the molecular subtypes of breast cancer are proved to be an independent predictor (p < 0.001) of axillary lymph node status. In previous studies, several nomograms have been developed to predict axillary lymph node status in breast cancer patients undergoing NAT [15–18]. These studies included clinical indicators such as ER, PR, HER2, and Ki67 which showed good performance as independent predictors. Of note, these conclusions are also consistent with the results of the present study. A recent large sample retrospective study of the relationship between NAT responses and the defined molecular subtypes identified that pCR was less likely in women with Luminal A sub-type and most likely in HER2-positive women who should receive anti-HER2 therapy [19] which is also confirmed in our study. Our results indicate that the molecular subtypes play a crucial role in the prediction of axillary lymph node involvement after NAT and are worthy of attention by clinicians.
Our study predicted the status of axillary lymph nodes through the diagnosis and changes of imaging examination before and after NAT. In our study, the US axilla, MRI axilla, and CT axilla are independent predictors (p < 0.001), and the MG axilla is not an independent predictor (p > 0.05). In previous studies on US, MG, MRI, and CT; US and MRI are found to be the best in predicting the status of axillary lymph nodes unlike MG, which could not accurately predict it [20, 21]. These findings are also consistent with the results of this study. Moreover, there are also studies on the establishment of nomogram prediction models through in-depth learning of US or MRI, or simply through clinical indicators. The AUC of the training cohort and validation cohort in the previous US-based deep learning nomogram model is 0.816 and 0.759 respectively [22]. Further, the MRI-based nomogram model had an AUC of 0.81 [23, 24], and the AUC of the clinical indicators-based nomogram model was 0.802 [25]. In our study, we used four kinds of imaging methods to establish the nomogram prediction model in combination with clinical factors. The AUC of the training cohort and the validation cohort is 0.832 and 0.947, respectively, higher compared to the above-mentioned studies. This indicates that the constructed nomogram model had good diagnostic performance and is better than previous nomogram studies which relied on single imaging indicators or only clinical indicators.
In addition, we also found that the change in the primary lesion of breast cancer could also predict the status of the axillary lymph node. We found that both MG breast post-chemo and CT breast post-chemo were independent predictors of axillary lymph node status after NAT. Previous studies have focused on the size of the primary lesion as a factor to predict the axillary lymph node status [26–28]. However, breast cancer usually shows a decrease in the number of tumor cells after NAT, which is not always reflected by volume. In this study, we included the changes in primary breast cancer before and after NAT and divided them into complete response and not complete response groups according to the RECIST criterion. We found that if the primary lesion reached CR, the probability of axillary lymph nodes reaching pCR was 60.4%, and if the primary lesion was not reaching CR, the probability of axillary lymph nodes not reaching pCR was 70.9%. This suggests that it is feasible to predict the status of axillary lymph nodes by assessing whether the primary lesion reaches CR or not. Interestingly, in our study, the primary changes reflected by US and MRI had no statistical significance for the prediction of axillary lymph node status (p > 0.05). We speculate that the sample size of this study is not large enough and further research is warranted to comprehensively understand this in the future.
Although the nomogram developed in this study showed better prediction performance than the existing prediction systems, some limitations remain. First, our study is limited to a single-center retrospective study, and it is essential to expand these investigations and use data from other centers for further external verification. Secondly, the sample size included in this study is relatively small, and hence it is necessary to further verify the model’s prediction performance in a larger sample size. Finally, because the main parameters of the model are clinical indicators and imaging results, it may be necessary to apply some specific techniques (such as immunodiagnostic biomarkers) to improve the accuracy of our nomogram. Future research addressing the above-said limitations is essential to validate our nomogram model for wider Utility.