Prognostic value of CC-chemokine receptor seven expression in patients with metastatic renal cell carcinoma treated with tyrosine kinase inhibitor

For patients with metastatic renal cell carcinoma (mRCC), therapeutic options have expanded significantly these years, since vascular endothelial growth factor (VEGF)-targeted tyrosine kinase inhibitor (TKI) drugs such as sunitinib and pazopanib have been established as first-line therapy [1]. Several clinical based prognostic models, for example the Heng’s risk criteria, have also achieved remarkable progress in mRCC patient survival prediction [2]. However, the objective response rates (ORRs) for most first-line TKI drugs were only around 30% [3], and the lack of validated molecular biomarkers impeded their personalized approach [4]. This was in contrast to many other tumor types, in which protein expression and mutation were used as basic accesses for drugs response and patient survival prediction [5, 6].

CC-chemokine receptor 7 (CCR7), a G-protein coupled receptor (GPCR) mostly expressed on immune cells, was initially regarded as an important regulator facilitating leukocytes homing to the lymphatic structures, where its two ligands CC-chemokine ligand 19 (CCL19) and CCL21 are constitutively expressed [7]. However, in recent years, aberrant high CCR7 expression has also been identified on several tumor types, linking to a potential invasive phenotype [8]. It has been suggested that CCR7 positive tumor cells could mimic the normal lymphocyte homing function and interact with lymph vessels, leading to subsequent lymph node specific metastasis [9].

Lymphatic and hematogenous disseminations were two regular metastasis pathways for malignancy. For mRCC, although the most common metastatic site was the lung, possibly via a hematogenous approach, local or distant lymph node involvement at diagnosis was not rare [10]. Patient receiving TKIs could also develop new lymph node metastasis during the treatment, leading to a progressive disease (PD). Several theories of TKI drug resistance emphasized an increase of tumor cell invasiveness after drug administration [11]. These processes mostly accompanied with tumor cell migration and matrix metalloproteinase-9 (MMP-9) mediated extracellular matrix degradation [12], which was similar to the CCR7 mediated lymph vessel intravasation process [8]. As VEGF targeted therapies mostly focused on blood vessels inhibition, whether they could enhance the possibility of mRCC metastasis through other pathways, such as CCR7 mediated lymph vessel invasion and therapy resistance, was not known.

Thus, here through immunohistochemistry (IHC), we retrospectively evaluated the CCR7 expression in 110 primary tumor specimens of mRCC patients treated with sunitinib and sorafenib. The result suggested a positive correlation of CCR7 expression with patient baseline lymph node metastasis and TKI drugs response. CCR7 high expression could predict a poorer overall survival (OS) and progression free survival (PFS) for mRCC patients after TKIs.

CCR7 was naturally a homeostatic chemokine receptor expressed on various subtypes of immune cells encompassing T cells, B cells, natural killer cells and dendritic cells, enabling them to circulate through the CCL-19/21 positive lymphatic highways [7]. Its expression on cancer cells was first recognized on hematogenous malignancies, in which the connection between high CCR7 expression and lymphoid organ involvement was discovered [21]. Subsequently, numerous laboratory studies confirmed this pro-invasion, mostly pro-lymph vessel metastatic function in various cancer types, including breast cancer, melanoma, non-small cell lung cancer, prostate cancer, head-and-neck cancer and gastrointestinal cancer [9]. Here, our results suggested that CCR7 also expressed on several RCC specimens and associated with various patient baseline characteristics (Table 1, Additional file 1: Figure S1).

The clinical prognostic value of CCR7 has been studied in several other cancer types. In a meta-analysis including 1697 gastric cancer patients, high CCR7 correlated with a worse 5-year overall survival rate [22]. Studies in melanoma and colorectal cancer also displayed similar results [23, 24]. In this study, we have found that high CCR7 staining intensity could be used as an adverse prognosticator for mRCC patients’ overall survival. Moreover, a new model integrating CCR7 expression into Heng’s risk criteria performed better than using Heng’s risk alone, and the adding prognostic value mostly came from the intermediate patient groups (Additional file 3: Table S2, Fig. 2a and b). This indicated that a substantial number of patients might switch between risk groups with a consequence for choice of treatment strategy after CCR7 status was considered. ROC analysis for the ccRCC patient group were also carried out, considering the poor performance of CCR7 in non-ccRCC patients (Fig. 2c and d).

For PFS analysis, to our knowledge, this study was the first to report an association between tumoral CCR7 expression and PFS in mRCC patients following TKIs. As the most widely used systemic therapy at present, TKI drugs only reached ORRs for about 30% for mRCC patients, and the theories of drug resistance was complicated [25]. It is increasingly evident that in some tumors, in which angiogenesis is thwarted genetically or pharmacologically, cancer cells could adapt by migrating more aggressively into normal tissue, based on several pre-existing invasion programmes such as epithelial-mesenchymal transition (EMT) and MMP2/MMP9 secretion [26, 27], or by switching on several distinctive programmes which were currently unknown [28]. Since the CCR7 mediated lymphatic specific migration and metastasis was also based on several above mentioned programmes [8, 29], and as a molecule which could give tumor itself survival signal besides [30], we hypothesized that CCR7 positive RCC cells might have a potential to migrate into the adjacent lymphatic tissue for survival after TKI drugs administration, subsequently leading to resistance and disease progression. As a result, our study did identify an independent significant adverse predictive effect of high CCR7 expression on mRCC patients’ PFS (Fig. 3b) and its association with poorer best drug response (Table 1, Fig. 3a). Patients’ baseline lymph node involvement status was also correlated (Table 1, Fig. 4a) and four patients who developed PD due to new lymph node metastasis all represented high CCR7 staining for their tumor tissues. All these results above indicated an impact of tumoral CCR7 expression on patients’ PFS and lymphatic involvement status, making this molecule a potential predictor for mRCC patients receiving TKIs.

The major limitations of this pilot study were its retrospective design and relatively small sample size, with patients from a single center and same ethnic background. Although central patient data review and bootstrap validation were performed for minimizing inter-observer and over-fitting bias, further external prospective validations were required, and related basic researches were needed for verifying our hypothesis. Samples from the metastatic site after TKI therapies might be excellent candidates for in-depth investigation. Besides, although we took two cores and six scans from each patient’s sample, intratumoral heterogeneity still might confound the results. Patients in this study received sunitinib or sorafenib as first-line therapy because other agents were not available in China at that time, and other VEGF-based TKI drugs such as pazopanib, axitinib and cabozantinib should also be taken into further consideration.

Our study indicated that high tumoral CCR7 expression correlated with potential lymphatic involvement and poor prognosis in mRCC patients treated with TKIs. This biomarker could also be combined with the Heng’s risk model for better risk stratification.