Primary tumor inflammation in gross tumor volume as a prognostic factor for nasopharyngeal carcinoma patients

Purpose The objective of this study is to investigate the prognostic value of primary tumor inflammation (PTI) in nasopharyngeal carcinoma (NPC) in the era of intensity-modulated radiation therapy (IMRT). Results PTI was observed in 376/1708 (22.0%) patients, and was present in the sphenoid sinus in 289/376 (76.9%), in the nasal cavity in 27 (7.2%), and in both places in 60 (15.9%). The estimated 4-year local relapse-free survival (LRFS), disease-free survival (DFS), overall survival (OS) and distant metastasis-free survival (DMFS) rates for PTI vs. non-PTI group were 89.2% vs. 96.1% (P < 0.001), 73.4% vs. 85.1% (P < 0.001), 85.0% vs. 92.1% (P < 0.001) and 83.6% vs. 91.4% (P < 0.001), respectively. After adjustment for these known prognostic factors, PTI was confirmed as an independent prognostic factor for LRFS (HR 2.152, 95% CI 1.318–3.516, P = 0.002), DFS (HR 1.581, 95% CI 1.204–2.077, P = 0.001) and DMFS (HR 1.682, 95% CI 1.177–2.402, P = 0.004). Conclusions Primary tumor inflammation was identified as a strong prognostic factor for patients with NPC in the era of IMRT and should be considered when devising future treatment strategies aimed at improving survival in NPC patients. Materials and Methods Data on 1708 patients with nonmetastatic, histologically-confirmed NPC treated with IMRT between November 2009 and February 2012 at Sun Yat-Sen University Cancer Center were retrospectively reviewed. Patient survival between PTI and non-PTI groups were compared.


INTRODUCTION
Worldwide, there were an estimated 84,400 new cases of nasopharyngeal carcinoma (NPC) and 51,600 deaths in 2011 [1]. NPC is an uncommon cancer with a very unique geographical distribution, with an age-standardized incidence rate of 20-50 per 100,000 males in south China but only 0·5 per 100,000 in Caucasian populations in 2011 [1]. Due to anatomic constraints and high radiosensitivity, radiotherapy is the only curative treatment for NPC. Despite its known limitations, the TNM staging system remains the most important prognostic factor for NPC patients [2]. Many other factors had been reported to have prognostic value, including plasma Epstein-Barr virus (EBV) DNA [3][4][5], primary tumor volume [6,7], pretreatment serum lactate dehydrogenase (LDH) levels [8] and apparent diffusion coefficient (ADC) [9].
Due to the special location and invasiveness of NPC [10], primary tumor inflammation (PTI) in gross tumor volume (GTV) is a commonly imaging feature in advanced T stage patients. Using magnetic resonance (MR) imaging, inflammation in GTV is seen as an area of high signal intensity on T2-weighted images, and as an area of low signal intensity on contrast material-enhanced T1-weighted images. The prognostic value of necrosis in cervical nodal, a subtype of inflammation in NPC patients, has been demonstrated [11], as has the prognostic role of necrosis in bladder cancer [12]. Therefore, it is reasonable to speculate that the inflammation in GTV may also have prognostic value in NPC.
As we know, the relationship between primary tumor inflammation in GTV and prognosis of NPC patients has not been studied. Hence, we conducted a large-scale retrospective study to evaluate the impact of PTI on the clinical features and survival outcomes of NPC patients based on MR imaging (MRI) results.

Patient failure patterns
The median follow-up time for the entire cohort was 49.9 months (range, 1.3-76.4 months), and 263 (15.4%) patients were lost to follow-up. Patterns of treatment failure and cause of death are summarized in Table 2

Subgroup analysis
Due to the unbalanced distribution of PTI in T classification, subgroup analysis according to T and N classification and overall stage was performed to further investigate the prognostic value of PTI ( Table 5). The survival outcomes for PTI patients classified as T3 were substantially poorer than those T3 patients in the no-PTI group (P = 0.001 for LRFS, P = 0.005 for DFS, P = 0.041 for DMFS), and were similar to those of patients classified asT4 in the no-PTI group (90.6% vs. 90.9 for LRFS, 76.6% vs. 77.8% for DFS, 86% vs. 86.7% for DMFS). Additionally, for patients with N1 disease, the presence of PTI markedly affected prognosis (P < 0.05 for all rates). However, the presence of PTI did not substantially affect the outcomes of patients with T4 and N2-3 disease (P > 0.05 for all rates).

DISCUSSION
To the best of our knowledge, this is the first largescale study to investigate the prognostic value of PTI in NPC. In the present study, we observed a relatively high incidence (22.0%) of PTI, especially in patients with advanced T stage. The results of this study revealed that PTI was an independent prognostic factor with regard to 4-year LRFS, DFS and DMFS for patients with nonmetastatic NPC in the era of IMRT. However, no significant difference was found in 4-year OS for these two groups.
Due to the anatomical specificity and invasiveness, inflammation is common in the sphenoid sinus and nasal cavity in advanced T stage NPC and often combines with necrosis and bacterial infections, which results in local hypoxia and radioresistance. This was also observed in head and neck cancers [13][14][15][16]. Moreover, numerous previous studies showed that hypoxia is also an adverse prognostic factor in many malignant cancers like lung, breast, uterine cervix, rectum, brain, soft tissue and renal cell [17][18][19][20][21][22][23]. This mechanism may also explain the unfavorable prognostic value of cervical nodal necrosis in NPC [11]. www.impactjournals.com/oncotarget  Total 59 108 Abbreviations: PTI = primary tumor inflammation.
a P values were calculated using chi-square or Fisher exact test as indicated.  Abbreviations: PTI = primary tumor inflammation; LRFS = local relapse-free survival; DFS = disease-free survival; OS = overall survival; DMFS = distant metastases-free survival; WHO = world health organization.
a P values were calculated using the log-rank test.
In our cohort, patients with PTI tended to be older than patients without PTI, indicating that age may adversely contribute to primary tumor inflammation. One reasonable explanation is that older patients are likely to be in worse physical condition. PTI patients were also at a more advanced clinical stage on average, and tumor volume was generally larger. A greater number of PTI patients were thus undergoing chemotherapy. The significant prognostic difference showed by univariate analysis between these two groups should originate from unbalanced TNM staging and other prognostic factors. Multivariate analysis revealed PTI was an prognostic factor for LRFS, DFS and DMFS but not for OS, which indicated that the follow-up time was insufficient, and should be longer in any similar studies in future.
Subgroup analysis revealed a difference in the prognosis of PTI patients with T3 or N1 disease. Due to the extremely low incidence of PTI, no clinical prognostic value in T1-2 or N0 patients was observed. Moreover, patients with T4 or N2-3 are at a higher risk of distant metastases, and the prognostic impact of PTI may be masked by other important prognostic factors. The survival outcomes of PTI patients with T3 disease were similar to those with T4 classification. Hence, we proposed that T3 stage should be divided intoT3a and T3b stage based on PTI. More intensive chemotherapy regimen may be needed for patients with PTI compared with patients without PTI .
Another reason for unfavorable prognosis of PTI patients may be due to the difficulty in determining an accurate GTV using IMRT. Inflammation in the sphenoid sinus and nasal cavity often mixed with tumor and made it difficult to establish the tumor margin. Hence, the tumor target would easily be left out. Therefore, a thorough pretreatment assessment of PTI patients undergoing IMRT should be performed, and accurate delineation of GTV should be warranted to reduce local recurrence.
The findings of our current study suggest that clinicians should pay particular attention to NPC patients with PTI in order to accurately delineate the tumor target. Induction chemotherapy could be applied to shrink the tumor bulk and minimize inflammation to assist identification of the tumor margin. Additionally, a better dose coverage and reduced toxicity from radiotherapy could be achieved after induction chemotherapy. Additionally, proton and heavy particle therapy could result in better prognosis [24].
The main limitation of our study was that the judgement of PTI was only based on MRI. However, this could not be avoided because pathological results from surgical resection are not available due to the special location of NPC. The retrospective nature and short followup time are also limitations that should be addressed in future studies, and additional clinical experiments are needed to establish the prognostic value of PTI. Abbreviations: PTI = primary tumor inflammation; LRFS = local relapse-free survival; DFS = disease-free survival; OS = overall survival; DMFS = distant metastases-free survival; HR = hazard ratio; CI = confidence interval. a Multivariate P-values were calculated using an adjusted Cox proportional-hazards model with backward elimination and the following parameters: age (≥ 50 y vs. < 50 y), gender (male or female), pathological type (type I or type II/III), PTI (yes or no), smoking (yes or no), drinking (yes or no), T classification, N classification, undergoing chemotherapy (yes or No). www.impactjournals.com/oncotarget

CONCLUSIONS
In summary, this study confirmed that PTI was an independent prognostic factor for LRFS, DFS and DMFS for patients with NPC in the era of IMRT. It is advised that T3 stage should be divided into T3a and T3b stage based on the presence of PTI, and different intense treatment protocols should be considered for patients with PTI. Further prospective clinical study should be warranted to confirm the results of this current study.

Patients
We retrospectively analyzed 1811 patients with newly diagnosed NPC that showed no evidence of distant metastasis, who were treated between November 2009 and February 2012 at Sun Yat-Sen University Cancer Center. Pre-treatment MR images of the nasopharynx and cervical region were thoroughly analyzed. Of the entire cohort, 103 (5.7%) patients without MRI results were excluded, which left 1708 (94.3%) patients for further investigation. This study was approved by the Research Ethics Committee of Sun Yat-Sen University Cancer Center, and informed consent was obtained from all patients.

Clinical staging
The routine staging process included a complete history and clinical examination of the head and neck region, direct fibre-optic nasopharyngoscopy, MRI scans of the skull base, neck and chest radiography, a whole-body bone scan, and abdominal sonography. Positron emission tomography (PET)-CT scans were also performed if clinical indicated. All patients received a dental evaluation before radiotherapy. All patients were restaged according to the 7th edition of the International Union against Cancer/American Joint Committee on Cancer (UICC/AJCC) system [25]. All MRI materials and clinical records were reviewed to minimize heterogeneity in restaging. Two radiologists employed at our hospital separately evaluated all of the scans and disagreements were resolved by consensus.

Diagnostic criteria for PTI
All patients underwent MRI scans using a 3 Tesla system (Trio Tim; Siemens, Erlangen Germany). Only patients with inflammation surrounding the tumor were included in this study, and patients with sinusitis not in the immediate vicinity of the tumor were excluded. Diagnostic criteria for primary tumor inflammation in MRI include an area of high signal intensity on T2weighted images, and an area of low signal intensity on contrast material-enhanced T1-weighted images, which is similar to the diagnostic criteria for lymph node necrosis ( Figure 2) [26,27].

Radiotherapy
All patients received intensity-modulated radiation therapy (IMRT) at Sun Yat-Sen University Cancer Center. Immobilization was carried out using a custom-made head-to-neck-thermoplastic cast with the patient's neck resting on a support. A high-resolution planning computed tomography scan with contrast was taken from the vertex to 2 cm below the sternoclavicular joint at a slice thickness of 3 mm. Target volumes were delineated slice-by-slice on treatment planning CT scans using an individualized delineation protocol that complies with International Commission on Radiation Units and Measurements report numbers 50 and 62. The prescribed doses were 66-72 Gy at 2.12-2.43 Gy/fraction to the planning target volume (PTV) of the primary gross tumour volume (GTVnx), 64-70 Gy to the PTV of the GTV of the involved lymph nodes (GTVnd), 60-63 Gy to the PTV of the high-risk clinical target volume (CTV1), and 54-56 Gy to the PTV of the low-risk clinical target volume (CTV2). All targets were treated simultaneously using the simultaneous integrated boost technique.

Chemotherapy
According to our institutional guidelines, prior to commencing treatment we recommended radiotherapy alone for stage I disease, concurrent chemoradiotherapy (CCRT) for stage II disease, and CCRT +/− neoadjuvant/ adjuvant chemotherapy for stage III to IVA-B disease. Neoadjuvant or adjuvant chemotherapy consisted of cisplatin with 5-fluorouracil, cisplatin with taxoids or cisplatin with 5-fluorouracil and toxoids, every three weeks for two or three cycles. Concurrent chemotherapy consisted of cisplatin given weekly or on weeks 1, 4 and 7 of radiotherapy.