Stomatitis and EGFR-Tyrosine Kinase Inhibitors: A Review of Current Literature in 4353 Patients

Conventional cytotoxic chemotherapy presents a wide range of side effects. These include oral toxicities such as hyposalivation/xerostomia, dysphagia, discomfort, taste alterations and mucositis. Oral complications are some of the most significant toxicities and are often a dose limiting effect causing dose delays and interruptions of cancer treatment [1]. For these reasons, research has focused on the study of new therapeutic aids. In the last 20 years there has been an explosion of knowledge in the field of tumor biology. For the first time, researchers have had at their disposal a series of increasingly sophisticated techniques for studying genes, their protein products, and the various aspects of the cell cycle. Thanks to the identification of molecules that interact with a specific defect, the approach to Antineoplastic pharmacology has radically changed, moving from a disease-based pharmacology to a guided cross-therapy on the molecular defect. The future of cancer therapy seems to be the “targeted therapy”. Unlike the classic chemotherapy approach, which acts on nonspecific mechanisms linked to the characteristics of all rapidly proliferating cells, including normal ones, “targeted therapy” acts on the mechanisms linked to the expression of oncogenes and tumor suppressor genes, based on the specific tumor promotion action, which results in the transformation of the cell from normal to pathological [2,3]. The increase in understanding of carcinogenesis processes has in fact allowed to identify an ever-increasing series of mutations in the genes that express particular enzymes involved in several "cascades" of intracellular signals, alterations capable of subverting the normal mechanisms of regulation that maintain the equilibrium of the cell (homeostasis), pushing it towards uncontrolled proliferation, and making it acquire characteristics of aggressiveness for the organism. The development of a molecular type drug capable of blocking these enzymes or of humanized monoclonal antibodies, which act on the chains of signals interfering with the receptors present on the cell surface, has radically changed the prognosis of several types of cancers [4]. EGFR is a member of the receptor tyrosine kinases ErbB family and is a cell surface molecule whose activation leads to an intracellular signaling cascade affecting invasion, apoptosis and angiogenesis. The structure of the EGFR family receptor members Abstract Conventional chemotherapy presents a wide range of side effects including oral toxicities such as hyposalivation, dysphagia, discomfort, taste alterations and mucositis. Oral complications often cause dose delays and interruptions of cancer treatment. EGFR is a member of the receptor tyrosine kinase ErbB family and a cell surface molecule whose activation leads to an intracellular signaling cascade promoting invasion, apoptosis and angiogenesis. Recent researches led to the development of a new drug class anti-EGFR, EGFR Tyrosine Kinase Inhibitors (TKI). The following review was performed to answer to the following question “Which is the rate of stomatitis in patients treated with EGFR TKI’s?” A systematic search was performed on the PubMed online database. Title and abstract of 102 potentially relevant studies were screened. Only 30 studies were included in the review. The overall incidence of stomatitis of any grade was 67.5% for erlotinib, 49.4% for afatinib, 40% for dacomitinib. These data showed a high rate of lower grade stomatitis. Indeed the rate of G1-G2 stomatitis was 59.3% in patients treated with erlotinib, 49.3% with afatinib and 35% with dacomitinib, while the rate of G3-G4 stomatitis was 15.3% in patients treated with erlotinib, 8.3% afatinib and 4.8% dacomitinib. Analysis of the reports about patients treated with EGFR-TKI showed a clear prevalence of stomatitis grade 1 or 2. These data differ from that of patients treated with conventional chemotherapy in which mucositis is predominantly of grade 3 or 4.


Introduction
Conventional cytotoxic chemotherapy presents a wide range of side effects. These include oral toxicities such as hyposalivation/xerostomia, dysphagia, discomfort, taste alterations and mucositis. Oral complications are some of the most significant toxicities and are often a dose limiting effect causing dose delays and interruptions of cancer treatment [1]. For these reasons, research has focused on the study of new therapeutic aids. In the last 20 years there has been an explosion of knowledge in the field of tumor biology. For the first time, researchers have had at their disposal a series of increasingly sophisticated techniques for studying genes, their protein products, and the various aspects of the cell cycle. Thanks to the identification of molecules that interact with a specific defect, the approach to Antineoplastic pharmacology has radically changed, moving from a disease-based pharmacology to a guided cross-therapy on the molecular defect. The future of cancer therapy seems to be the "targeted therapy". Unlike the classic chemotherapy approach, which acts on nonspecific mechanisms linked to the characteristics of all rapidly proliferating cells, including normal ones, "targeted therapy" acts on the mechanisms linked to the expression of oncogenes and tumor suppressor genes, based on the specific tumor promotion action, which results in the transformation of the cell from normal to pathological [2,3]. The increase in understanding of carcinogenesis processes has in fact allowed to identify an ever-increasing series of mutations in the genes that express particular enzymes involved in several "cascades" of intracellular signals, alterations capable of subverting the normal mechanisms of regulation that maintain the equilibrium of the cell (homeostasis), pushing it towards uncontrolled proliferation, and making it acquire characteristics of aggressiveness for the organism. The development of a molecular type drug capable of blocking these enzymes or of humanized monoclonal antibodies, which act on the chains of signals interfering with the receptors present on the cell surface, has radically changed the prognosis of several types of cancers [4]. EGFR is a member of the receptor tyrosine kinases ErbB family and is a cell surface molecule whose activation leads to an intracellular signaling cascade affecting invasion, apoptosis and angiogenesis. The structure of the EGFR family receptor members  *Timmers et al. [29] did not report the grade of stomatitis. **Irigoyen et al. [21] and Krishnan et al. [23] reported the incidence rates limited to grade 3 and 4 treatment-related toxicities, for this reason data about cases of stomatitis and stomatitis grade 1 and 2 are lower than real monoclonal antibodies and small molecules EGFR tyrosine kinase inhibitors [6]. This unique class of orally administered small molecule therapeutics has been employed into the standard of care treatment in a wide variety of cancer types including non small cell lung cancer, breast cancer, colon, pancreas, head and neck and GIST cancer [5]. Tyrosine kinase inhibitors may help patients to avoid some of the most common toxicities of traditional cytotoxic chemotherapy where toxicities usually involve bone marrow. Even if the Tyrosine Kinase Inhibitors are promising, they induce a variety of side effects such as diarrhea and mucositis, rash and paronychia due to the fact that epidermal growth factor is expressed on nearly all normal cells.
In most cases mucositis induced by this class of inhibitor used in monotherapy corresponds to a moderate erythema with limited and superficial ulcers occurring shortly after treatment introduction. This form of mucositis sometimes has the appearance of lesions aphthouslike, although these lesions are less typical than those provoked by mTOR inhibitors. They can involve all areas of the not keratinized mucosa. When these drugs are used in combination with cytotoxic therapies they can cause deeper mucosal ulcerations [7]. The terms "oral mucositis" and "stomatitis" are often used interchangeably to indicate oral complications of anti-cancer therapy, but they do not refer to the same process. Oral mucositis is a Medical Subject Headings term that describes inflammation of the oral mucosa due to chemotherapeutic agents or ionizing radiations, while stomatitis is a less specific term used to describe any inflammatory condition of oral tissue [8].

Materials and Methods
The following review was performed to answer the following question "Which is the rate of stomatitis in patients treated with EGFR TKI's?" A systematic search was performed on the PubMed online database using a combination of MESH terms and free text words: "afatinib" (free text) OR "erlotinib" (MESH) OR "gefitinib" (free text) OR "lapatinib" (free text) combined through the Boolean operator AND with the key words "stomatitis" (MESH) OR "oral mucositis" (MESH).
Only studies fulfilling the following inclusion criteria were considered eligible for inclusion in this study: 1. Performed on human subjects.  2. Reporting about the use of an mTOR inhibitor.
3. Writ-ten in the English language.
4. Reporting about the incidence of stomatitis or oral mucositis.

More than 4 papers referring to a single agent.
Case reports and studies on animal model were excluded from this study. No restrictions were applied to the year of publication.
For each study, the following records were extracted: name of the first author, year of publication, number of patients enrolled, type of disease treated, number of events recorded, and grade of the events reported. To simplify the process of data extraction, an ad hoc extraction sheet was used. In addition, data were independently extracted by two authors (LLM and CA) and checked in a joint session. The paper reporting about "gefitinib" and "lapatinib" were excluded due to an insufficient number of cases of oral adverse events reported.

Results
Titles and abstracts of 102 potentially relevant studies were screened ( Figure 1); 54 studies of these were excluded because they did not report the inclusion criteria. In the second round, 48 studies were read full text but only 30 were included in the review for the exclusion of papers referring to agents with few studies (<5 studies). Of the included study 17 referred to erlotinib, 10 to afatinib and 5 to dacomitinib. Of these 1 referred both to erlotinib and afatinib, 1 referred both to erlotinib and dacomitinib. For erlotinib 17 studies were analyzed (Table 1). A total of 1.497 patients were treated with erlotinib. The overall incidence of stomatitis of any grade with treatment was 67.5% (1.010 patients). Studies reported data about grade of stomatitis for 1.297 patients and 770 cases were grade 1/2 (59.3%) and 199 were grade 3/4 (15.3%). For afatinib 10 studies were analyzed (Table 2). A total of 1.664 patients were treated with afatinib. The overall incidence of stomatitis of any grade with treatment was 49.4% (822 patients). Studies reported data about grade of stomatitis for 1.611 patients and 795 cases were grade 1/2 (49.3%) and 134 were grade 3/4 (8.3%). For dacomitinib5 studies were analyzed (Table 3). A total of 1.192 patients were treated with dacomitinib. The overall incidence of stomatitis of any grade with treatment was 40% (476 patients) and 418 cases were grade 1/2 (35%) and 58 were grade 3/4 (4.8%).

Discussion
The aim of targeted therapy is to achieve a preferential localization of an antineoplastic agent directly in the region of disease and subsequently an increase in local concentration. EGFR inhibitors are a class of targeted drugs. The Epidermal Growth Factor Receptor (EGFR) is a transmembrane receptor Tyrosine Kinase of the ErbB family which is abnormally expressed in many epithelial tumors. The first attempt to target EGFR dates over 20 years ago when Mendelsohn et al. [9] proposed EGFR as a target for cancer therapy. Small molecules tyrosine kinase inhibitors compete with ATP binding to the Tyrosine Kinase domain of the receptor inhibiting Tyrosine Kinase activation and thus blocking EGFR signaling pathways. The differences between different agents of this class are mainly on their potency against the different members of the HER-receptor family and their ability to inhibit a single receptor type.
Tyrosine kinase inhibitors were considered to have nonoverlapping toxicities if compared with cytotoxic chemotherapy. Studies reveal that the most common toxicities associated with tyrosine kinase inhibitors are neutropenia, thrombocytopenia, skin toxicities, hypertension, fatigue, hemorrhage and arterial thrombotic event [10].
Oral toxicities include mucositis, xerostomia, dysphagia and pharyngitis. Results of literature analysis showed that the rate of stomatitis of all grades in patients treated with erlotinib is 67.5%, in patients treated with afatinib is 49.4% and in patients treated with dacomitinib is 40%. The review of the literature showed a high rate of lower grade stomatitis (G1 to G2) while the onset of severe stomatitis (G3 to G4) was lower. Indeed in patients treated with erlotinib the rate of G1 to G2 stomatitis was 59.3%, in patients treated with afatinib  the rate of G1 to G2 stomatitis was 49.3% and in patients treated with dacomitinib the rate of G1 to G2 stomatitis was 35%. The rate of G3 to G4 stomatitis in patients treated with erlotinib was 15.3%, in patients treated with afatinib was 8.3% and in patients treated with dacomitinib was 4.8%. Due to the heterogeneity of the data collected and the different methods of classification of oral manifestations due to EGFR inhibitors it was not possible to collect data regarding the treatment modalities as we did for mIAS [11]. The main limitations of these new molecular drugs are represented by the very high cost and by the fact that these compounds are often effective on a limited percentage of patients who, in most cases, cannot yet be identified.
To overcome this difficulty, it is necessary to identify valid predictive biomarkers of response, whose presence or activation is able to indicate the sensitivity to a specific therapy targeted. Moreover it must be considered the concurrence with other types of chemotherapeutic drugs associated in chemotherapeutic regimens.
Although the action specificity of these drugs causes less frequently the adverse effects of this class of drugs and a less debilitating effect on the patients than those of classical chemotherapy, there are still problems related to adverse reactions of this type of agents. The most common are those of oral/dermatological type linked to drugs with an inhibitory action on the growth factor of the epidermis (EGFR). In some cases, however quite rare, the level of these undesirable effects may be such as to force the abandonment of therapy [12]. As regards the treatment of stomatitis caused by EGFR-TKI literature reports that patient should follow a simple oral care regimen which consists of brushing the teeth and tongue with a soft-bristle brush or if unable to use a toothbrush with foam swab or a piece of gauze. Oral care should be performed every 2 hr to 3 hr in case of mild stomatitis and every 1 hr to 2 hr in case of severe stomatitis. In case of mouth sensitivity patients should gargle with benzydamine rinse 3 times daily as needed. For grade 1 stomatitis, patients can use triamcinolone in dental paste applied 2 to 3 times daily with the addition of oral erythromycin or mynocicline in case or grade 2. The triamcinolone is substituted by clobetasol ointment in case of grade 3 stomatitis [13,14].

Conclusion
The analysis of data of this review showed a clear prevalence of grade 1-2 stomatitis in patients treated with EGFR-TKI.