Anemia Is a Predictive Factor for Overall Survival Rate in Patients With Non-small Cell Lung Cancer Treated With Stereotactic Body Radiation Therapy

Purpose: Anemia has been associated with poor prognosis in patients with cancer across several cancer types. It has been identied as a prognostic factor in patients with non-small cell lung cancer (NSCLC) who have undergone surgery or chemoradiotherapy. However, there are only a few reports that have evaluated the prognostic signicance of anemia in patients with NSCLC undergoing stereotactic body radiation therapy (SBRT). Material and Methods: A total of 77 patients were enrolled this study. The pretreatment hemoglobin (Hb) levels, within 2 weeks before SBRT, were available for all patients. The median age of the participants (56 men, 21 women) was 80 (range, 50-90) years. The median Hb level was 12.8 (range, 7.8-18.3) g/dL. The median follow-up period was 24 (range, 1-87) months. Results: Local recurrence was observed in 8 (10.4%) cases during the follow-up period. The 1- and 2-year local control (LC) rates were 94.8 and 86.4%, respectively. Seventeen (22.1%) patients died during the follow-up period. The 1- and 2-year overall survival (OS) rates were 93.1 and 85.2%, respectively. Univariate analysis identied anemia and body mass index as signicant prognostic factors for predicting OS. On multivariate analysis, anemia was conrmed to be the only signicant factor (p = 0.02469). Conclusion: Our data suggest that anemia is a prognostic factor for predicting the OS rate in patients with early-stage NSCLC treated with SBRT.


Introduction
Among all cancers, lung cancer had the highest estimated incidence and mortality rates in 2018 worldwide [1]. An estimated 2,094,000 people worldwide were diagnosed with lung cancer in 2018, resulting in 1,761,000 deaths. Stereotactic body radiation therapy (SBRT) is an important treatment option for early-stage non-small cell lung cancer (NSCLC) with results comparable to surgery [2]. Nagata Y et al. reported favorable outcomes in both operable and inoperable NSCLC cases treated by SBRT [3]. Chang JY et al. reported good results of SBRT in a pooled analysis of patients enrolled in two phase-III trials that compared surgery with SBRT [4].
Anemia has been associated with a poor prognosis in patients with cancer across various types of cancer [5][6][7][8][9][10]. In patients with NSCLC who undergo surgery [11][12][13] or radiation therapy or chemoradiotherapy [14][15][16][17], anemia has been reported as a poor prognostic factor. However, there is limited literature available on the prognostic signi cance of anemia in patients with NSCLC undergoing SBRT. The purpose of this study was to evaluate the association between pretreatment anemia and prognosis in patients with NSCLC treated with SBRT.

Methods And Materials
Patients This retrospective study was conducted with the approval of our institutional review board, and all patients provided written informed consent before treatment. The inclusion criteria were as follows: patients with localized NSCLC, N0M0 disease, who were clinically inoperable or refused surgery, and were treated with SBRT, and for whom the hemoglobin (Hb) levels were available within 2 weeks before SBRT. Between September 2009 and September 2019, 77 patients meeting the inclusion criteria were identi ed and included in the study. Cases where the pathological diagnosis could not be con rmed were treated as NSCLC if the joint conference of respiratory surgeons, pulmonologists, radiologists, and radiation oncologists came to that consensus. Planning and irradiation Before radiation treatment planning, patients were evaluated by four-dimensional computed tomography (4DCT) using Somatom (SIEMENS, Germany) for the amount of movement of the tumor caused by respiration. For 4DCT, real-time positioning management (RPM) system (Varian Medical Systems, USA) was used. Patients with respiratory motion of the tumor ≥ 1.0 cm were planned for the implantation of a ducial marker which were implanted by bronchoscopy near the tumor. For every such patient, three markers were implanted.
All patients underwent the CT scan under light exhalation breath-hold, and 4DCT were also performed using RPM. The slice thickness was 1.0 or 2.0 mm.
Patients were immobilized using Vac-Loc Cushion (CIVCO Medical Solution, USA) with both their arms up. The clinical target volume (CTV) was de ned as equal to the gross tumor volume (GTV). In patients with implanted ducial markers, the internal target volume (ITV) was equal to the CTV. In contrast, summation of the GTVs de ned at every respiratory phase of the 4DCT gave the ITV in patients without the ducial marker. The planning target volume (PTV) was generated by adding 5 mm around the ITV. In principle, the prescribed dose for peripherally situated tumors was 50 Gy in 5 fractions until September 2016 and 48 Gy in 4 fractions after October 2016. The tumors with a central location near organs at risk were treated with 60 Gy in 8 fractions. A central tumor was de ned as a tumor whose distance from the proximal bronchial tree was ≤ 2 cm. The dose was prescribed to the isocenter. Leaf margins were modi ed to cover the PTV by 80% of the prescribed dose. The treatment for patients without ducial marker was performed under light free breathing.

Evaluation
The medical charts were reviewed and data pertaining to age, sex, performance status (PS), body mass index (BMI), operability, smoking history (current or past vs. never smoker), the presence of diabetes mellitus (DM), the presence of pathological or cytological con rmation, tumor diameter, irradiation method (respiratory gated or not), and pretreatment Hb levels were obtained.
The survival periods were calculated from the completion of the SBRT.
The associations between Hb levels and other categorical variables were tested using Mann-Whitney U test and the correlation with continuous variables was tested by Spearman's rank correlation coe cient. Local control (LC) and overall survival (OS) rates were calculated using the Kaplan-Meier method, and group comparisons were made using the log-rank test. Univariate and multivariate Cox proportional hazard regression models were used to estimate the LC and OS rates. Variables for which the p-values were < 0.10 in the univariate analysis were included in the multivariate analysis. Receiver-operating characteristic (ROC) analysis was performed to determine the optimal cut-off values for the pretreatment Hb level. A p-value < 0.05 was considered to indicate a statistically signi cant difference.

Results
The patient characteristics are shown in Table 1 The association between Hb levels and other parameters are shown in Table 2. The Hb levels were signi cantly lower in patients with lower BMI than in patients with a higher BMI. There was a weak positive correlation between Hb level and BMI. Also, the Hb levels were signi cantly higher in patients with a smoking history than in those without a smoking history. There was no signi cant correlation observed between Hb levels and the other parameters.

Outcome
The median follow-up period was 24 (range, 1-87) months. Local recurrence was observed in 8 (10.4%) cases during the follow-up period. The 1-and 2-year LC rates were 94.8 and 86.4%, respectively. In univariate analysis, there was no signi cant prognostic value of the LC rate (Table 3).
Seventeen (22.1%) patients died during the follow-up period with 7 of them dying from lung cancer. The 1-and 2-year OS rates were 93.1 and 85.2%, respectively. Univariate analysis found anemia and BMI as signi cant factors for predicting the OS rates. Multivariate analysis con rmed anemia as the only signi cant independent prognostic factor (p = 0.02469) ( Table 4). The optimal cut-off values of Hb level, as determined by ROC analysis, was 11.6 g/dL. The OS rates with lower Hb level was signi cantly poor that that with higher Hb level (p = 0.00767) (Fig. 1). The 1-and 2-year OS rates for higher and lower Hb groups were 96.1% and 88.3%, and 84.4% and 76.0%, respectively.

Discussion
There was a weak positive correlation between Hb level and BMI. Hb levels in patients with lower BMI were signi cantly lower than in the group with higher BMI. This is explained by the fact that Hb level is correlated with nutritional status. That is, patients with poor nutrition had low Hb levels and low BMI. Hb levels were signi cantly higher in patients with smoking history than in those without smoking history. This was because most smokers were men. In fact, men (92.5%) had a signi cantly higher smoking history than women (40.0%) (Fisher's exact test, p = 0.00000735). Median pretreatment Hb levels in men and women were 13.1 (range, 8.9-18.3) and 11.4 (range, 7.8-14.6), respectively. Because men had signi cantly higher Hb levels than women (p = 0.0187), and most smokers were men, smoking history could not be directly correlated with elevation of Hb levels.
In the recent years, there have been many reports indicating that pretreatment Hb levels signi cantly correlates with the outcomes in several types of cancer [5][6][7][8][9][10]. These reports include various treatment modalities, such as surgery, chemotherapy, radiation therapy, and combination of them. Though various outcome measures were reported the OS rates were most commonly reported. In patients with NSCLC, pretreatment Hb level was a signi cant predictor of prognosis in patients with treated by surgery or chemoradiotherapy [11][12][13][14][15][16][17]. However, literature about correlation between anemia and outcome in patients of NSCLC undergoing SBRT is lacking. To the best of our knowledge, the report by Shaverdian N et al, is an only report on the given subject [20]. They reported that pretreatment Hb levels correlated signi cantly with OS rate and non-local disease progression, but not with LC rate. Their results were comparable to our results, where we found pretreatment Hb levels to correlate signi cantly with OS rate but not with the LC rate.
Anemia is considered to cause of intratumor hypoxia [21]. Because tumor hypoxia is one of the causes of radioresistance, patients with anemia are expected to have a lower LC rate post radiation therapy. However, in our results, pretreatment Hb levels correlated signi cantly with OS rate but not with the LC rate.
There are a few hypotheses to explain this result. Hypoxia inducible factor (HIF) was discovered from hepatocellular carcinoma cell lines as a factor that could induce hypoxia dependent erythropoietin [22]. HIF-1 induced the vascular endothelial growth factor, platelet-derived growth factor B, and basic broblast growth factor, and improved hypoxia [23]. In tumors, HIF-1 gets activated in response to hypoxia [24]. Therefore, it cannot be concluded that the oxygen concentration in the tumor of patients with a low serum Hb level will be lower than that of patients with a high serum Hb level. Additionally, HIF causes epithelial-mesenchymal transition and also promotes metastasis [25]. Hypoxia promotes tumor growth and progression to more aggressive character due to neo-angiogenesis, gene mutation, apoptosis inhibition, and free radical generation [21,[26][27][28].
SBRT is a relatively new treatment method. Many prognostic factors have been recently reported in patients with NSCLC who undergo SBRT, such as tumor size and standardized uptake value on 18F-uorodeoxyglucose positron emission tomography [29,30]. Pretreatment Hb level is an easily derived and cost effective blood parameter. Therefore, the utility of pretreatment Hb as a predictive prognostic indicator is high in the clinical setting.

Conclusion
Our data suggests that anemia is correlated with OS rates in patients with early-stage NSCLC who are treated with SBRT. Abbreviations SBRT; stereotactic body radiation therapy, NSCLC; non-small cell lung cancer, Hb; hemoglobin, 4DCT; four-dimensional computed tomography, CTV; clinical target volume, GTV; gross tumor volume, ITV; internal target volume, PTV; planning target volume, PS; performance status, BMI; body mass index, DM; diabetes mellitus, LC; local control, OS; overall survival, ROC; receiver-operating characteristic, HIF; hypoxia inducible factor.

Declarations
Ethical approval and Consent to participate This retrospective chart review study involving human participants was in accordance with the ethical standards of the institutional and national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The Human Investigation Committee (IRB) of Yamaguchi University approved this study (H2019-101).

Consent for publication
Not applicable Availability for supporting data The datasets used and analyzed during the current study are available from the corresponding author on reasonable request.

Competing interests
The authors declare that they have no competing interests.

Funding
The authors did not receive support from any organization for the submitted work.
Author's contribution    Table 3 The results of univariate analysis for local control rate.  Table 4 The results of univariate and multivariate analysis for overall survival rate. Overall survival rates for high and low hemoglobin groups