1. IntroductionIn recent years, development of biological targeted therapies and immune checkpoint inhibitors has redefined the treatment for many cancers [1]. In order to avoid the severe adverse effects of conventional chemotherapy agents that are cytotoxic to all replicating cells, targeted therapies were designed to inhibit or minimize the development of cancer cells by attenuating, at the same time, the side effects of the therapy [2,3,4].Inhibitors of angiogenesis are among the most common targeted therapies. Angiogenesis refers to the formation of new blood vessels, which facilitates the growth of the tumors as well as the spreading of the tumor though invasion of the vessels and entry into circulation. The main goal of antiangiogenic therapy is to inhibit pro-angiogenic molecules, such as Vascular Endothelial Growth Factor (VEGF), and, by doing so, to suppress the formation of new vessels [5,6]. Angiogenesis inhibitors are either monoclonal antibodies such as bevacizumab and aflibercept, or tyrosine kinase inhibitors (TKIs) such as sunitinib, sorafenib and pazopanib.Several adverse effects have been associated with antiangiogenic therapy. Despite the fact that targeted therapies seem to display less or milder toxicities than conventional chemotherapy, several possible treatment complications have been reported including hypertension, thromboembolic events, cardiac dysfunctions, hypophosphatemia, thrombocytopenia, infections, chronic pain and skin conditions. Further, an increasing number of oral side effects of targeted therapies has been emerging, including medication related-osteonecrosis of the jaw (MRONJ) and oral mucositis, which may have a significant impact on patients’ quality of life [4,7,8,9,10,11]. Other possible complications of targeted therapies in the oral cavity include lichenoid lesions, xerostomia, dysgeusia and dysphagia [4,12].MRONJ is a severe complication in cancer patients that manifests with many possible clinical signs and symptoms, including exposed bone, fistula, inflammation with or without suppuration, ulcers, soft and hard tissue necrosis, and edema. Pain, incapability of receiving food, paresthesia and trismus are complications arising due to jaw necrosis [13,14,15]. Since the first reports by Marx et al. in 2003 [13], MRONJ has been mainly associated with antiresorptive therapy (or with the so-called bone-targeting agents) that include bisphosphonates and denosumab [14,15]. However, there is an emerging incidence of MRONJ development in patients receiving antiresorptives in combination with antiangiogenic agents and/or mTOR inhibitors over the past few years [11]. More recently, MRONJ cases have been observed following administration of angiogenesis inhibitors without concurrent antiresorptives [11,14,15]. Among the antiangiogenic agents reported in the literature, bevacizumab and sunitinib were found to be the most common ones causing MRONJ [11].Pazopanib is an oral small-molecule multi-kinase inhibitor that primarily inhibits VEGF receptor-1, -2 and -3, platelet endothelial growth factor receptor-α and -β, and the stem-cell factor receptor c-kit. Although pazopanib was developed as a therapeutic agent against various tumors, it is currently approved in many countries specifically for advanced soft-tissue sarcoma [11]. In addition, in October 2009, pazopanib was approved from FDA as first-line treatment for patients with advanced renal cell carcinoma (RCC) [12]. Reported side effects of the drug include diarrhea, nausea/vomiting, headache, loss of appetite, weight loss, altered sense of taste, temporary hair loss and/or change in hair or skin color. In addition, gingival bleeding related to pazopanib is very rare but a possible side effect in patients treated for RCC [8,10], while only a few cases report pazopanib or the similar drug axitinib as the main cause of MRONJ appearance [9,10,11,16].

The aim of the study is to present three cases of oral toxicities (one case of gingival bleeding and two cases of MRONJ) related to antiangiogenic treatment with pazopanib in patients with metastatic RCC (mRCC).

3. DiscussionAngiogenesis inhibitors, as well as inhibitors of molecular pathway of mammalian target of rapamycin (mTOR), are nowadays the mainstay of treatment for mRCC [10,17,18]. In fact, angiogenesis is upregulated via the production of VEGF in order to supply more oxygen due to hypoxia in cancer microenvironment. In cases of RCC, VEGF production is constantly increased. Antiangiogenic agents in mRCC patients target VEGF signaling, leading to inhibition of tumor-induced angiogenesis and, as a result, tumor growth suspension [17]. In late 2009, pazopanib obtained approval for patients with mRCC.Even though angiogenesis inhibitors do not cause complications at a level similar to conventional chemotherapy, they still manifest various adverse events. The prevalence of oral toxicities of any grade in patients with mRCC is about 4% for pazopanib versus higher incidence for sunitinib and sorafenib (38% and 28%, respectively). In addition, regression of symptoms requires only dose reduction and not discontinuation of the drug [19]. It should be mentioned that oral adverse events in these patients are often underestimated, since patients rarely undergo an oral examination by an expert clinician. As a consequence, the reported prevalence of oral adverse events is low and diagnosis is frequently rendered at more advanced stages.Among the oral adverse events of angiogenesis inhibitors, the most important ones, in particular from an oral surgery standpoint of view, are mucocutaneous bleeding and delayed wound healing. Hemorrhagic diathesis could be attributed to changes in vascular permeability caused by the antiangiogenic effects, and more often it manifests as nasal bleeding [1]. The incidence rate of bleeding events is up to 20–40% for bevacizumab versus 9–14% for pazopanib [1,20]. On the other hand, delayed wound healing could be explained since agents that inhibit VEGF affect vascular nourishment and re-epithelialization [21].In the present study, our first case described gingival bleeding that could be, at least in part, attributed to the antiangiogenic effect of pazopanib. The blood counts were normal, pazopanib was the only administered medication that could affect hemostasis and oral hygiene was poor predisposing to gingivitis and local infections. Similar cases of gingival bleeding in patients receiving antiangiogenics have been published in the literature [21,22]. In these published cases, gingival bleeding was accompanied by necrotizing ulcerative gingivitis (NUG). Patients were treated conservatively with antibiotics, and, similar to our case, oral antiseptics and discontinuation of the angiogenesis inhibitor for a period of time. All signs and symptoms subsided and patients returned to their oncologic treatment.MRONJ is a drug-related complication, observed in patients receiving mainly agents with antiresorptive and antiangiogenic properties. Initially, the complication was described in patients receiving antiresorptives, first bisphosphonates and later denosumab. Subsequently, several reports were published about MRONJ development in patients receiving bisphosphonates and concomitant bevacizumab or sunitinib. In these cases, a higher prevalence and worse clinical features were noticed, probably due to a cumulative toxicity profile [21].In more recent years, there have been several reports about MRONJ in antiresorptive-naïve patients who had received only angiogenesis inhibitors. The majority of these cases were related to bevacizumab and sunitinib administration. Two of our cases demonstrated MRONJ development in antiresorptive naïve patients who received pazopanib as monotherapy (Case 2) or pazopanib followed by sunitinib (Case 3). There is another case published in the literature describing MRONJ development in a patient receiving pazopanib followed by everolimus [9].The pathophysiology of MRONJ has not been fully clarified. Different hypotheses have been proposed to explain the pathogenesis of this complication. A quite dominant theory implicates the effect of the medication on macrophages, especially in antiresorptive-naïve patients as in our cases. Macrophages are derived from monocytes originating from bone marrow, have characteristics similar to osteoclasts and express VEGF receptors on their surface. Antiangiogenic agents cause reduction in macrophage numbers and activity by blocking VEGF pathway and, as a result, increase the risk for infections and tissue necrosis causing host defense impairment [7,10,22]. In addition, the interference in the natural angiogenesis, leading to reduced blood supply to the jaws and inhibition in bone repair, facilitates bacterial contamination of the exposed bone [8].MRONJ in antiresorptive-naïve patients seems to have approximately the same predilection for gender, age, location (mandible) and dominant symptom (pain) as MRONJ in patients receiving antiresorptives and similar to our cases. A difference between the two conditions is the predominant cancer diagnosis, which in antiangiogenics-related MRONJ is advanced gastrointestinal cancer, followed by mRCC, whereas most cases of anti-resorptive-induced MRONJ are seen in breast cancer and multiple myeloma patients [23]. Furthermore, the mean time to MRONJ onset is shorter for angiogenesis inhibitors (38.8 weeks) than that of antiresorptives (136 weeks) [19]. On the other hand, the prognosis seems to be better in MRONJ associated with non-antiresorptive agents since resolution is more frequent (62% vs. 50%) and with shorter average time (6.75 vs. 8.2 months) [11]. These differences could be attributed to the shorter half-life and lower cumulative doses of angiogenesis inhibitors [11].As far as treatment is concerned, conservative management is more commonly selected for MRONJ, according to the AAOMS position paper, and surgical approach is limited in persistent stage III that has failed to respond to conservative treatment [14,19]. In the cases presented here, Case 2 was treated conservatively, including local applications of ozone oil. According to the literature, ozone oil is produced by oxygen, which has a positive impingement on wound healing. It is reported that ozone oil is widely used as an antimicrobial agent and to promote wound healing due to its tissue repair properties [24]. As for Case 3, conservative treatment was also selected. Antibiotics, chlorhexidine and chamomile mouth rinses were used, the latter traditionally used as a treatment for many inflammatory diseases. Several literature reports refer to chamomile as a medical treatment with multiple applications in daily life; its antiaging, anticancer, anti-inflammatory, antioxidant, and antimicrobial properties establish it as a useful therapeutic approach in tissue repair process [25,26].

Pazopanib as well as other novel targeted therapies are widely used in clinical practice with remarkable effects, but they also provoke several adverse events. Health care professionals should be alerted to recognize initial and faded symptoms. A thorough oral and dental examination should be performed in all patients who receive or are about to receive angiogenesis inhibitors in order to maintain optimal oral health, reduce oral microbial load and achieve early diagnosis and prompt treatment of any complications, if needed.