NPC is a chemo-sensitive tumor and palliative chemotherapy plays an important role in disease control and prolonging survival in the metastatic setting. Standard treatment comprises chemotherapy with platinum doublets of drugs such as gemcitabine, paclitaxel, and 5-FU together with cisplatin/carboplatin. For treatment-naive patients who receive platinum-based chemotherapy, response rates as high as 80% and a median survival of 12 to 18 months may be achieved [15]. Radiotherapy is usually employed for palliative purpose for metastatic cancer, such as alleviation of pain and relieving symptoms. However, some studies have demonstrated that intensive local therapy could prolong OS in treatment-naive metastatic cancers, reflecting that certain subgroup of patients with newly mNPC may obtain long-term survival after aggressive treatment [16-19]. Recently, Chen et al [2] randomized 126 mNPC who responded to PF regimen to chemotherapy plus locoregional radiotherapy or chemotherapy alone in a phase III randomized trial. It is revealed that the addition of radiotherapy improved survival outcomes, with 2-y OS of 76.4% and PFS of 35%. It seems that the sensitivity to chemotherapy is critical to select the patients who could benefit from locoregional radiotherapy. However, it remains unknown about the efficacy of locoregionl intensity-modulated radiotherapy (IMRT) combined with other chemotherapy regimens, such as taxane/gemcitabine-containing regimens.
Gemcitabine plus cisplatin (GP) is considered as the standard first-line treatment for recurrent and metastatic NPC,evidenced by the phase III trial demonstrating that GP regimen prolonged median progression-free survival from 5.6 months to 7 months compared with classical PF regimen [20]. Taxane combined with cisplatin, such as TPF/TP regimen, is also proved to be effective in locoregionally advanced NPC [21, 22]. In our center, taxane/gemcitabine combining with cisplatin regimens have been routinely recommended for mNPC since 2008. This study analyzed the treatment results of 118 who responded to GP or TPF/TP regimen and then treated with locoregional IMRT. The data presented in this study demonstrated that taxane/gemcitabine plus cisplatin combined with IMRT represented an effective treatment for mNPC, with OS and PFS being 44% and 34.2%, respectively. 2-year PFS of 53.6% in our study is better than that reported by the randomized trial. The superiority in PFS may be contributed to the novel drug taxane and gemcitabine. Thus, taxane/gemcitabine plus cisplatin combined with IMRT has the potential to improve survival outcomes in newly mNPC with mild toxicity and is worthy of further investigation in prospective studies.
In the present study, pretreatment lymphocyte count was found to be an independent prognostic factor for both PFS and OS in the univariate and multivariate analysis. Among patients with high pretreatment ALC, only one patient (1/58, 1.7%) experienced locoregional relapse, while eight patients (8/60, 13.3%) in low ALC group had locoregional failure. Patients with high lymphocyte count also experienced lower rate of distant progression. Lymphocytes, an essential component of host immunity, play a critical role in the destruction of residual tumor cells and micrometastases. The effect of chemotherapy and radiotherapy is found to be associated with the function of lymphocytes. Its prognostic value has been reported in the locoregional advanced NPC without distant metastasis. Liu et al. [13] collected serial lymphocyte counts and survival data from 413 NPC patients, and demonstrated that low mini-ALC during treatment predicted a worse PFS and OS. To our knowledge, this study is the first study to investigate the role of lymphocyte as prognostic factor in NPC with synchronous metastasis. We did not analyze the role of serial lymphocyte counts during or after treatment since the lymphocyte count are vulnerable to chemoradiation and can be increased by some supportive treatments, such as dexamethasone and granulocyte-macrophage colony-stimulating factor (GM-CSF). The confounder factors would reduce the capacity of ALC to reflecting status of immunity and impede us to investigate prognostic value of ALC. Baseline ALC can be more feasibly and consistently obtained and thus the predicting value based on it would be more likely to be repeated and generalized.
PD-1 inhibitor therapy has revolutionized the treatment of cancers, including NPC [6]. In the management of recurrent or metastatic NPC, pembrolizumab and nivolumab, are now used as standard second line agents [23, 24]. The combination of camrelizumab with cisplatin and gemcitabine used as first-line therapy in 23 patients with recurrent or metastatic demonstrated an objective response of 91% [25]. Trials investigating PD-1 inhibitor therapy in the de novo mNPC are ongoing. However, the predictive biomarkers of PD1 inhibitor therapy other than PD-L1 expression, which is of limited utility in NPC, are much in need. Since the mechanism of anti-PD1 antibodies is thought to be dependent on the activity of functional T lymphocytes, it is rational to hypothesize that the efficacy of anti-PD1 antibodies would be compromised in patients with low lymphocyte count. Ho et al [26] treated thirty-four recurrent/metastatic head and neck patients with either nivolumab or pembrolizumab alone and found that lower ALC was significantly associated with lack of clinical benefit. Therefore, baseline ALC, not only predicting the outcomes of chemoradiation, but also relevant to efficacy of PD-1 inhibitor therapy, should be considered in future prospective studies on PD-1 inhibitor therapy for mNPC.
mNPC patients is a heterogeneous group of patients exhibiting a wide range of survival outcomes. M1 classification cannot be used to accurately predict survival outcomes among mNPC patients. The subdivision of M1 stage based on involved organs and the number of lesions has been proposed. Zou et al [17] subdivided the M1 stage into three categories: M1a, oligo metastasis without liver involvement; M1b, multiple metastases without liver involvement; and M1c, liver involvement irrespective of metastatic lesions. They found that the M1a and M1b classification of NPC may benefit from aggressive and potentially curative treatment, while chemoradiotherapy did not benefit patients in M1c. Shen et al [14] classified M1 stage into three groups: M1a, single lesion confined to an isolated organ or location except the liver; M1b, single lesion in the liver and/or multiple lesions in any organs or locations except the liver; and M1c, multiple lesions in the liver. The subdivision by Shen et al [14], adopted in this study, was found be an independent factor for OS, but not for PFS. Patients with M1b had significantly worse OS than patients with M1a (HR=4.107, P<0.001), and for patients with M1c accounting for 7 patients, there is a trend of inferior survival compared with M1a. It is demonstrated that the subdivision of M1 is still relevant to prognosis even in chemotherapy-sensitive patients who can benefit from radical locoregional RT and should be considered in tailoring the treatment for mNPC.
Other treatment-related factors, such as the cycle of chemotherapy [18, 19] and radiation dose [27,28] were found to be related to treatment outcomes in previous studies. However, none of these was found to be an independent prognostic factor in our study. This inconsistency could be partially explained by that the previous studies have a large heterogeneity in the treatment modality and patients recruited. In our study, patients received relatively uniform treatment. All the patients received 4-6 cycles of chemotherapy. Equal to or more than 60Gy of total dose was given to all the patients and 89(75.4%) patients received 66-70.4 Gy. Local treatment of metastatic lesions was associated with worse survival outcomes in our study, which can be explained that local treatments of metastatic lesions were mainly employed to for palliative purpose to alleviate local symptoms in patients with progressive diseases.
This study was subject to several limitations. Firstly, due to the respective nature and limited sample size, all analyses are subject to the influences of selection bias and potential imbalances in unquantified variables. Secondly, our data did not analyze the role of lymphocyte subpopulations, as lymphocyte having both pro- and anti-cancer function [29, 30]. Furthermore, circulating EBV DNA load was unknown in the majority of patients. The predicting modal based on lymphocytes and circulating EBV DNA may be more accurate to individualized treatments for mNPC, which is our future research direction. Additionally, it cannot be determined from our data whether lymphopenia is a truly predictive biomarker of aggressive chemoradiotherapy, or simply a global prognostic biomarker. Finally, our data were exclusively obtained from one center; therefore, these results must be validated by other datasets.
In conclusion, taxane/gemcitabine plus cisplatin combined with IMRT represents an effective treatment modality for synchronous mNPC. Baseline ALC is an independent prognostic factor for PFS and OS. The subdivision of M1 is still correlated with OS in the chemo-sensitive patients receiving locoregional IMRT. Further prospective studies are warranted to investigate the treatment alternative and potential prognostic factors found in this study.