Precise therapy is a recently intensively pursued approach at the molecular level and the role of genetic test in guiding chemotherapy and evaluating prognosis is increasingly significant. The genes ERCC1, RRM1, TUBB3, TYMS, and TOP2A have been widely concerned for their relevance to the efficacy of chemotherapeutic drugs. Nucleotide excision repair (NER) plays a major role in DNA damage repair caused by platinum drugs [14]. The expression product of ERCC1 gene can limit or regulate NER [15] and its level reflects the level of overall NER [16]. Therefore, the high expression of ERCC1 means that the NER is strengthened and the efficacy of platinum drugs is weakened. In these studies [4,17-19], it was confirmed that patients with high expression of ERCC1 were resistant to platinum drugs and their prognosis was poor. Ribonucleotide reductase consisting of two subunits, RRM1 and RRM2, is the rate-limiting enzyme in the DNA synthesis pathway [20], which has a significant influence in DNA damage repair. The RRM1 subunit encoded by the RRM1 gene is the main target of gemcitabine. Related studies have shown that [5,6] high expression of RRM1 is associated with gemcitabine resistance. Microtubules are involved in many key cellular processes including cell division. Paclitaxel drugs can stabilize microtubules, prevent mitotic and further prompt tumor cell death. However, β-III tubulin encoded by TUBB3 gene can decline the stabilizing effect of anti-microtubule drugs on microtubules, induce drug resistance and reduce the efficacy [21]. This view was confirmed in studies of Kamath et al. [7] and Scambia G et al. [22]. Thymidylate synthase (TS) encoded by the TYMS gene is a key enzyme in the synthesis of pyrimidine nucleotides. TS is a major target enzyme of fluorouracils. It exerts anticancer effects by inhibiting the synthesis of deoxythymidylate (dTMP) and further affecting DNA synthesis and repair [23]. In clinical studies of breast cancer [24], colorectal cancer [25], lung cancer [26] and other tumors, patients with low expression of TYMS have better chemotherapeutic response to fluorochemical drugs and a longer median survival time. The topoisomerase 2A encoded by the TOP2A gene is not only a key enzyme that accelerate transient breaks in the DNA but also a target for anthracyclines. Anthracycline specifically binds to TOP2A and reduces its degradation. So the damaging effect of TOP2A on DNA is enhanced and tumor cells eventually died[27]. The studies [9,28] of anthracycline chemotherapy for breast cancer showed that patients with low expression of TOP2A gene had poor efficacy and poor prognosis.
The mRNA expressions of above genes in 70 patients of precise group were detected by MBL technology. High expressions of ERCC1 and RRM1 were observed in 4.3% and 5.7% of the group respectively, while high expressions of TUBB3 and TYMS were observed in 27.1% and 22.9% of the group respectively. Low expressions of TOP2A were observed in 38.6% of the group. The results indicate that some patients may have primary drug resistance of some chemotherapy drugs.
To the best of our knowledge, there is no study on combined detection of above genes for guiding the chemotherapy of breast cancer. We retrospectively analyzed the survival data of 140 breast cancer patients. The results showed that DFS in the precise group was 10.3 months longer than that of the classic group (P=0.039), and the 5-year disease-free survival rate was higher than that of the classic group (87.3% vs 73.8%). In our OS analysis, we found that the OS of the precise group was 6 months longer than that of the classic group (P=0.031), and the 5-year overall survival rate was higher than that of the classic group (94.3% vs 84.2%). Moreover, the Kaplan-Meier survival curves of DFS and OS showed that the overall prognosis of the precise group was better than that of the classic group (Log-Rank test: P=0.039, 0.031). To explore whether the precise chemotherapy strategy under the guidance of genetic testing is an independent prognostic factor for breast cancer, the relationship between all baseline variables and survival data initially was investigated via univariate analysis. Those variables of P<0.1 were incorporated into the Cox hazards regression model for multivariate analysis. The Cox regression analysis revealed that precise chemotherapy strategy can reduce the risk of recurrence or metastasis (HR=0.389, 95% CI: 0.153, 0.989, P=0.047). Furthermore, metastasis of axillary lymph nodes was an independent risk factor for DFS and poor endocrine therapy compliance was an independent risk factor for DFS and OS.
In terms of drug safety, patients generally tolerated and successfully completed 6-8 cycles of chemotherapy. Although various adverse reactions did occur during chemotherapy, they could be controlled by symptomatic treatment, reduction of drug dosage, intermittent or termination of chemotherapy. There was no grade 5 adverse event in this study. The incidence of grade 2 or 3 palpitations and chest tightness in precise group was significantly lower than that in classic group (12.9% vs 27.1% P=0.035). This may be related to that the classic regimen contained anthracyclines and the precise group selectively used it according to the TOP2A gene expression. In addition, there was no statistically significant difference in the incidence of other adverse events (nausea, vomiting, diarrhea, constipation, mucositis, myelosuppression, liver toxicity, fatigue and hand-foot syndrome) between the two groups.
The method selected chemotherapy regimens according to each patient's genetic characteristics can reduce the occurrence of drug resistance, show positive effects and provide new ideas and clinical evidences for individualized treatment of breast cancer. However, our study also has some limitations. Firstly, the study is a single-center study with an inherent selection bias and sample size is not enough large, which may draw different conclusions with previous studies. Secondly, the gene expression was detected using the MBL technology, but not confirmed by immunohistochemistry with normal breast tissues or para-carcinoma tissues as control. However, the results of this study are reliable, because MBL technology is currently a mature gene detection technology which has been widely applied in the prognosis prediction and individualized treatment of some tumors [10,29-33].Additionally, above genes are not only a single biological function. Further research is essential to explore whether they are closely related to other chemotherapeutic drugs. Finally, the application of testing technology may result in an increase of treatment costs. And whether the benefit-cost ratio is maximized should be treated individually. In summary, it is still necessary to further investigate the guiding significance of ERCC1, RRM1, TUBB3, TYMS, TOP2A and other genes in precise therapy through clinical studies of multi-center, large sample, addition of control samples, immunohistochemistry confirmation.