Background
The frequent inactivation of the Von Hippel Lindau (
VHL) gene in clear cell renal cell carcinoma, leading to increased levels of hypoxia inducible factor 1 (HIF1) and vascular endothelial growth factor (VEGF), provides the rationale for treatment with antiangiogenic receptor tyrosine kinase (rTKI) inhibitors. Since the reporting of the first positive clinical trial [
1], showing an overall survival benefit from a rTKI, sunitinib has become mainstay first line treatment for patients with metastatic renal cell carcinoma (mRCC). Although objective response rates are reported for around 50% of the patients, development of resistance to the treatment is a major problem [
2]. Clearly, a subset of patients does not benefit from treatment with sunitinib, and side effects are frequent. Interestingly, hypertension is a common side effect of angiogenesis inhibitors and has been associated with improved treatment response [
3]. In the research community, considerable effort has been made to identify and validate predictive biomarkers of response to sunitinib treatment, but so far, no biomarkers have been established as useful in clinical decision making and treatment planning.
There is increasing evidence to support an important role of systemic inflammation in development and progression of RCC [
4], as recently substantiated by positive results from a clinical trial with the PD-1 inhibitor nivolumab in mRCC [
5]. VEGF does not only stimulate tumor associated angiogenesis, but also plays an important role in the local immune response in wounds (physiologic) and tumors (pathologic) by inducing accumulation of immature dendritic cells, myeloid-derived suppressor cells, regulatory T cells, as well as by inhibiting the migration of T lymphocytes to the tumor [
6]. Thus, it is relevant to also explore biomarkers primarily associated with inflammatory responses in the search for predictive markers for response to anti-VEGF therapy.
C-reactive protein (CRP) is an established biomarker for systemic inflammation, available in most clinical datasets, and provides prognostic information in several cancers including RCC [
7]. Another biomarker of inflammation, neutrophil-to-lymphocyte ratio (NLR), adds prognostic information in RCC, and was recently suggested as a predictive marker of response to sunitinib in mRCC [
8]. In the present trial we investigated the predictive value of serum markers, including CRP and NLR, in an unselected prospective patient population treated with sunitinib for mRCC. In addition, we report on toxicity and health related quality of life (HRQoL) data.
Discussion
Until recently, palliative surgery, radiation therapy and chemotherapy were the only treatment options for metastatic RCC (mRCC), and primary therapy resistance, reduced quality of life and short survival were major challenges in this patient group. Currently, three major categories of systemic treatment exist for the largest subgroup of mRCC, the clear cell carcinomas: cytokines and immune checkpoint inhibitors, anti VEGF targeted drugs and mTOR inhibitors [
12]. The two latter of these new treatment options have emerged based on recent knowledge of the pathogenesis of clear cell renal cancer. The von Hippel-Lindau (VHL) tumor suppressor gene is lost or mutated in 60–90% in sporadic cases [
13] and is a major contributor to development of this cancer. Loss of VHL leads to a chronic stress response state in the cells trough high levels of HIF1-α, a transcription factor for a number of stress response proteins, including vascular endothelial growth factor (VEGF). In addition to being a potent angiogenic growth factor, VEGF plays a role in the local immune response in wounds and tumors by inducing accumulation of immature dendritic cells, myeloid-derived suppressor cells, regulatory T cells, as well as by inhibiting the migration of T lymphocytes to the tumor [
6]. Renal cell cancer is regarded as highly immunogenic and angiogenic tumors, supporting VEGF as a promising target for treatment. The VEGF receptor inhibitor Sunitinib is currently first line treatment for mRCC [
12], but a significant portion of the patients do not respond, and the search for good predictive markers of response has been disappointing so far. Whereas most focus in the search for predictive markers has been on angiogenesis, less focus has been on markers of immune responses. In the current study, we evaluated readily available clinical and biochemical markers, associated with systemic inflammation, for their association with response to sunitinib.
C-reactive protein (CRP) is an acute-phase protein that increases rapidly following interleukin-6 secretion by macrophages and T cells following infection, inflammation and cancer [
14]. CRP is a negative prognostic marker in most cancers. In the present study we found normal CRP to be a possible predictive factor of response. Whereas 41% of the patients with normal CRP at baseline experienced an objective response, this was the case for only 5% of patients with CRP levels at baseline above normal. CRP was also associated with PFS and OS supporting its role as a prognostic marker as well, and this is in line with previous reports [
15‐
17]. Our finding supports the results of a recent study by Fujita et al. where normal level of CRP at baseline was an independent predictive marker of response by multivariate analysis [
15]. In a retrospective study of 200 patients treated with sunitinib 61% of patients with normal CRP responded vs 32% of patients with elevated CRP [
18]. In our trial, CRP was correlated to several factors including other markers of systemic inflammation such as high platelet counts, anemia as well as tumor load and performance status. Thus, CRP might represent a marker of disease burden identifying a patient subpopulation with poor prognosis, less likely to respond. Nevertheless, the significant association with response rates suggests that CRP might be a useful marker, in addition to other clinical and biochemical features to consider prior to initiation of systemic treatment. IL-6 is an important tumor-promoting protein associated with stress responses, inflammation and angiogenesis [
19]. Through its major downstream target STAT3 several tumor promoting pathways are activated, including HIF1-α and VEGF [
19]. Moreover, IL6 have direct stimulating effect on endothelial cells, and has been implicated in resistance to anti-VEGF therapy [
20]. Being closely correlated to IL6 expression, increased CRP levels might therefore be a surrogate marker of IL6 driven disease, again being associated with expression of multiple angiogenic factors [
21], thus less responsive to specific anti-VEGF treatment like sunitinib. Our results indicate that an inflammatory response, defined by high CRP is associated with poor response to sunitinib and poor prognosis in these patients. The effect of sunitinib on inhibiting the angiogenesis supporting and immunosuppressive effect of VEGF, thus seem to be more pronounced in patients with a non-inflammatory state defined by normal CRP.
The neutrophil-to-lymphocyte ratio (NLR) is also a marker of systemic inflammation in cancer patients and was found to add prognostic [
22] and predictive [
8] information in RCC in retrospective studies. Like CRP, NLR is readily available in standard blood samples in a regular clinical setting. Our NLR counts were comparable to what has been reported in other clinical datasets. Although significantly associated with CRP, we did not find a statistically significant association with sunitinib response or survival. The significant correlation with performance status and tumor load suggests that NLR is a nonspecific marker of disease burden. Still, due to relatively small sample size and low statistical power, our data must be interpreted carefully.
Treatment induced early hypertension (eHTN) was not significantly associated with treatment response in our dataset. In our patient population, the baseline blood pressure was slightly higher when compared with the clinical trial population studied by Rini et al. [
3], and 52% of our patients were hypertensive at baseline. Still, the number of patients recorded as having sunitinib induced eHTN after cycle 1 and 2, using the same criteria, was nearly the same (~80%). eHTN at week 12 was associated with improved survival, but this is most likely due to the fact that the responders in the study stayed on treatment long enough to develop hypertension. Even if pharmacodynamically interesting, as eHTN occurs
after sunitinib initiation it is not going to be an applicable predictive marker in the clinic.
Our finding that higher baseline HRQoL symptoms score is prognostic for PFS and OS in treatment with Sunitinib is in line with the earlier report by Cella et al. [
23]. In that report, however, a different QoL tool was used. Herrmann et al. demonstrated by using EORTC QLQ-C30, that “global QoL” was prognostic for PFS [
24]. Our study did not confirm this finding. In general, there were only small changes in HRQoL scores form baseline to 12 weeks. Herrmann et al. also showed a relatively small change in the different HRQoL scales after 12 weeks [
24]. This could be due to the administration of Sunitinib (4 weeks on/ 2 weeks off), with subsequent remission of eventual treatment induced symptoms. There are indications that long-term survivors might retain a good HRQoL over years, as described by Carmichael et al. [
25].
A major challenge in studies exploring predictive markers of treatment response in clinical data-sets is the fact that most of the candidate predictive markers are prognostic as well, thus significantly correlated with PFS and OS independent of the treatment given. Combined predictive and prognostic markers are best evaluated in two-arm trials. In single arm trials such as ours, response rates according to RECIST are superior to PFS and OS as primary end-point when assessing predictive markers of treatment response. Many biomarker studies in mRCC have been performed retrospectively in data-sets from large clinical trials, and these patients are frequently positively selected and do not optimally reflect the normal patient population. The strength of our study is the prospective design and the “Real-World” patient population enrolled, reflecting a normal clinical setting. When compared with large retrospective multicenter studies as well as smaller single-center studies, the majority of our patients were in the poor risk group according to IMDC criteria. Whereas the portion of poor-risk patients varies between 18 and 33% in comparable studies [
8,
11,
15], 46% of our patients belonged to this group. In addition, all patients were in confirmed clinical and/or radiological progression at the time of inclusion. Accordingly, patients with very slow progression or stable metastases were observed without systemic treatment and screened for inclusion in the study only after confirmed disease progression. In comparison with clinical phase III trials, PFS and OS were lower in our patients. Compared with the adverse events reported in clinical trials [
26], the frequency of toxicity from sunitinib in metastatic renal cell cancer recorded in our study was similar, or somewhat less frequent. Especially, the hematological toxicity including anemia, neutropenia, thrombocytopenia and lymphopenia was less frequent in our trial, although using the same criteria (CTCAE v. 3.0). The most likely explanation for this discrepancy is that we assessed adverse events, including laboratory, every 6 weeks, where most of the patients were off the drug in the 4 + 2 weeks cycle.
In addition to the lack of a control group, our study has some weaknesses. First, the number of patients included is low and thereby the study lacks the significant power to detect minor differences in response rates between groups based on the biomarkers under investigation. Thus, our finding should be validated in an independent and larger cohort of patients. Second, CRP and NLR are non-specific markers of inflammation and angiogenesis, and further studies are required to identify the key regulators controlling the systemic responses to metastatic disease. In this report, we focused on biomarkers available in standard clinical blood samples routinely used in the clinic. Further studies of candidate biomarkers in serum and plasma, such as IL6 and IL8 are ongoing.