First report of a complete pathological response of a pelvic GIST treated with imatinib as neoadjuvant therapy

Pathologic complete response to neoadjuvant imatinib of a gastric stromal tumor with concomitant mutations in KIT: A case report and literature review

Key clinical message

We report the first case of pathologic complete response (pCR) to neoadjuvant imatinib in a gastric stromal tumor harboring KIT mutations in both exons 11 and 9. The significance of this co-occurrence is unknown and might increase the responsiveness of gastrointestinal stromal tumors (GISTs) to imatinib.

Abstract

pCR of GIST to neoadjuvant imatinib is rare. We report a case of pCR to neoadjuvant imatinib in a gastric stromal tumor that harbored co-occurrence of multiple KIT mutations in exons 11 and 9. This co-occurrence in exons 9 and 11 is the first to be reported in the English literature.

Complete response of advanced rectal gastrointestinal stromal tumors after imatinib treatment: A case report and literature review

RATIONALE

Patients with rectal gastrointestinal stromal tumors (GISTs) who achieve a complete response (CR) with imatinib therapy have rarely been reported in the literature. Moreover, no treatment guidelines have been established for rectal GIST patients with CR after imatinib treatment, warranting further studies.

PATIENT CONCERNS

A 51-year-old man presented to our outpatient clinic in October 2013 with complaints of difficulty to defecate and a change in stool characteristics. During digital rectal examination, a mass was palpated within 5 cm from the anal verge. Contrast-enhanced computed tomography revealed a 8.1 × 7.2-cm rectal mass with significant enhancement during the arterial phase.

DIAGNOSES

A diagnosis of GIST was established after conducting needle biopsy and immunohistochemistry staining.

INTERVENTIONS

Imatinib therapy (400 mg/d, oral administration) was immediately started. When the patient achieved clinical CR (cCR), the oncologist recommended the patient to continue imatinib treatment.

OUTCOMES

At 7 months after imatinib administration, the patient achieved cCR. As suggested by the oncologist, the patient continued to receive imatinib treatment after cCR. After 13 months, the patient spontaneously stopped imatinib. Finally, tumor recurrence was observed 7 months later.

LESSONS

Surgery remains the mainstay of treatment for advanced rectal GIST patients who achieve cCR after imatinib treatment. Close follow-up and continuous imatinib treatment are indicated in patients who cannot undergo surgery.

Advances and Challenges on Management of Gastrointestinal Stromal Tumors

Gastrointestinal stromal tumors (GISTs) originate from interstitial cells of Cajal and account for over 5,000 newly diagnosed cases in the United States. The discovery of activated KIT and PDGFRA mutations and introduction of imatinib revolutionized the treatment strategy and opened up the new era of target therapy for solid tumors. Although surgery remains the primary modality of treatment for curative purpose, almost half of the patients experienced disease recurrence. Tailoring (neo)-adjuvant treatment with imatinib is ongoing to meet the need for an effective therapy. Currently, two drugs (sunitinib and regorafenib) have obtained Food and Drug Administration approval for GISTs after imatinib failure. However, most of the patients eventually progress due to primary or secondary resistance. Deeper understanding of the molecular mechanisms will guide us to develop personalized strategies in the future. Discussion in this review includes current standard management and the most recent advances and multiple ongoing clinical trials with different approaches. This review will provide further steps to be taken to conquer refractory disease.

Combined Therapy of Gastrointestinal Stromal Tumors

Radical surgery is the mainstay of therapy for primary resectable, localized gastrointestinal stromal tumors (GIST). Nevertheless, approximately 40% to 50% of patients with potentially curative resections develop recurrent or metastatic disease. The introduction of imatinib mesylate has revolutionized the therapy of advanced (inoperable and/or metastatic) GIST and has become the standard of care in treatment of patients with advanced GIST. This article discusses the proper selection of candidates for adjuvant and neoadjuvant treatment in locally advanced GIST, exploring the available evidence behind the combination of preoperative imatinib and surgery.

Indications for surgery in advanced/metastatic GIST

Gastrointestinal stromal tumours (GISTs) are a relatively rare entity and often present as a locally advanced tumour or with metastatic disease. Complete surgical resection is the only means of cure in localised disease; however, imatinib therapy has greatly advanced the management of GIST and is established as both an adjunct to surgery in high-risk cases and as principle therapy in metastatic disease. Surgery in advanced GIST has undergone a renaissance in recent years with the potential for a combined treatment approach with either neoadjuvant imatinib in locally advanced primary disease or as an adjunct to imatinib in those with metastases or recurrent disease. Neoadjuvant imatinib can render a locally advanced primary GIST resectable, allow less invasive procedures or promote preservation of function, especially if the tumour is located in an anatomically difficult position. The role of surgery in metastatic or recurrent disease is more controversial and case selection is critical. The potential benefit is difficult to quantify, although surgery may have a limited favourable impact on progression-free survival and overall survival for those patients whose disease is responding to imatinib or those with limited focal progression. Patients with imatinib resistant disease should not be offered surgery unless as an emergency where palliative intervention may be justified.

Laparoscopic sphincter-preserving surgery (intersphincteric resection) after neoadjuvant imatinib treatment for gastrointestinal stromal tumor (GIST) of the rectum

BACKGROUND

Gastrointestinal stromal tumors (GISTs) of the rectum are rarely found, and radical surgery such as abdominoperineal resection would be necessary for large rectal GIST. On the other hand, therapy for GIST has changed significantly with the use of imatinib. Neoadjuvant imatinib therapy may reduce tumor size and may potentially prevent extended surgery. Moreover, when sphincter-preserving surgery is carried out laparoscopically, it can be performed as minimally invasive surgery with preservation of the anus.

METHODS

From 2008 to 2011, five patients with rectal GIST were treated in our hospital. All patients received preoperative imatinib treatment (400 mg/day) and underwent laparoscopic sphincter-preserving surgery after 4-12 months of this treatment.

RESULTS

Initial median tumor size was 31 mm (range, 24-88). At the time of operation, the median tumor size was 24 mm (range, 11-52). Sphincter-preserving surgery was performed in all patients. Three patients underwent laparoscopic intersphincteric resection (ISR), and two patients underwent transanal full-thickness local resection and recto-anal anastomosis following laparoscopic ISR. Macroscopically complete resection was achieved, and microscopically, the resection margin was not involved of residual tumors. The median duration of postoperative hospital stay was 16 days (range, 13-30). No recurrence occurred in all patients during 1 to 4 years.

CONCLUSIONS

The present study suggests that neoadjuvant imatinib therapy might be effective to prevent extended surgery for rectal GIST, and laparoscopic sphincter-preserving surgery is safe and technically feasible. We recommend a combination of neoadjuvant imatinib therapy and laparoscopic ISR for locally advanced rectal GIST.

Neoadjuvant imatinib in locally advanced gastrointestinal stromal tumors (GIST): the EORTC STBSG experience

BACKGROUND

Preoperative imatinib therapy of locally advanced GIST may facilitate resection and decrease morbidity of the procedure.

METHODS

We have pooled databases from 10 EORTC STBSG sarcoma centers and analyzed disease-free survival (DFS) and disease-specific survival (DSS) in 161 patients with locally advanced, nonmetastatic GISTs who received neoadjuvant imatinib. OS was calculated from start of imatinib therapy for locally advanced disease until death or last follow-up (FU) after resection of the GIST. DFS was calculated from date of resection to date of disease recurrence or last FU. Median FU time was 46 months.

RESULTS

The primary tumor was located in the stomach (55%), followed by rectum (20%), duodenum (10%), ileum/jejunum/other (11%), and esophagus (3%). The tumor resection after preoperative imatinib (median time on therapy, 40 weeks) was R0 in 83%. Only two patients have demonstrated disease progression during neoadjuvant therapy. Five-year DSS/DFS rates were 95/65%, respectively, median OS was 104 months, and median DFS was not reached. There were 56% of patients who continued imatinib after resection. Thirty-seven GIST recurrences were diagnosed (only 5 local relapses). The most common mutations affected exon 11 KIT (65%). Poorer DFS was related to primary tumor location in small bowel and lack of postoperative therapy with imatinib.

CONCLUSIONS

Our analysis comprising the largest group of GIST patients treated with neoadjuvant imatinib in routine practice indicates excellent long-term results of combined therapy in locally advanced GISTs.

The predictive value of steatosis in hepatitis C virus infection

Steatosis is a complication of hepatitis C virus (HCV) infection and the mechanisms of its development are complex, involving viral and host factors. Steatosis that is prevalently viral is associated with HCV genotype 3, and steatosis that is prevalently metabolic is associated with non-3 genotypes. Viral steatosis is correlated with the level of HCV replication, whereas metabolic steatosis is related to insulin resistance. The two types of steatosis have a different impact on HCV disease and may have an additive effect. HCV infection is a multifaceted disease with hepatic and extrahepatic manifestations. There is a body of evidence indicating that HCV-related steatosis plays a role in many HCV manifestations and, thus, the presence of steatosis is a predictive factor for the development of such events. The current data show that HCV-related steatosis predicts an advanced liver disease and a more rapid progression of fibrosis, as well as an increased risk of development of hepatocellular carcinoma. Moreover, the presence of steatosis in a HCV patient has a high predictive value that the subject may have or may develop insulin resistance, diabetes and metabolic syndrome. Recently, a strict association between HCV-related steatosis and development of atherosclerosis has been demonstrated. In addition, steatosis negatively impacts response rate to interferon-based treatment, even in HCV genotype-3 infection. Therapeutic strategies to improve steatosis and, consequently, response to standard antiviral therapy and outcome of disease are wanted. The authors summarize current knowledge of impact of steatosis on the above reported clinical conditions associated with HCV infection.

Metabolic alterations and chronic hepatitis C: treatment strategies

INTRODUCTION

Chronic hepatitis C (HCV) infection is considered a metabolic disease. It is associated with a specific metabolic syndrome, HCV-associated dysmetabolic syndrome (HCADS), consisting of steatosis, hypocholesterolemia and insulin resistance/diabetes. These metabolic derangements contribute to a decrease in sustained virological response (SVR) to pegylated-interferon-α-ribavirin as standard of care (SOC), and are associated with progression of liver fibrosis.

AREAS COVERED

The review, highlighting the impact of HCADS and metabolic syndrome components of HCV disease progression and SOC, discusses current knowledge and perspectives on metabolic therapeutic strategies aimed at improving SVR rate of SOC for chronic hepatitis C.

EXPERT OPINION

HCV, features of HCADS and of metabolic syndrome may coexist in the same patient, thus all components of the metabolic syndrome must be assessed to individualize treatment. The results of therapeutic trials evaluating metabolic strategies combined with current SOC indicate that weight loss is a critical part of treatment which will improve both disease outcome and therapeutic response to SOC. Similarly, statins seem to improve response rate to SOC representing, once confirmed to be safe, an important therapeutic tool for HCV-infected patients. Findings from studies using insulin sensitizers combined with SOC are not conclusive and do not justify the use of this class of drugs in clinical practice.

Pathologic complete response with neoadjuvant imatinib for locally advanced pelvic GIST

There are few data that show pathologic complete response (pCR) to imatinib treatment in gastrointestinal stromal tumors (GISTs). We describe a case of a patient with pCR of a pelvic, locally advanced, high-risk GIST who was treated with neoadjuvant imatinib and ultimately underwent a conservative procedure. A 48-year-old male presented with a pelvic mass 10 cm in diameter. Biopsy revealed a gastrointestinal stromal tumor of rectal origin. Although it was considered initially resectable, an extensive procedure would have been necessary for complete resection. Treatment with imatinib was initiated, resulting in partial response. The patient remained on imatinib for over 15 months, maintaining stable disease. Radical prostatectomy with anal sphincter preservation was performed. Pathological report revealed no viable neoplastic cells. The use of imatinib was held for 6 months after the surgery. At a follow-up 15 months after surgery, the patient had no evidence of disease. Our report may help to guide future studies of neoadjuvant imatinib for large pelvic or rectum GISTs that are initially considered unresectable.

Role of surgery combined with kinase inhibition in the management of gastrointestinal stromal tumor (GIST)

BACKGROUND

Surgery is the standard treatment for primary, gastrointestinal stromal tumor (GIST); however, surgical resection often is not curative, particularly in large GIST. Five years after complete removal of their tumor, approximately half of treated patients relapse. Imatinib, an oral tyrosine kinase inhibitor (TKI), is first-line treatment in patients with metastatic or unresectable GIST. It has resulted in durable objective responses or stable disease in 84% of patients and is well tolerated. The efficacy of imatinib in advanced GIST has created interest in a variety of potential multimodal approaches to management that combine surgery with systemic therapy.

RESULTS

Recently, a large, randomized, Phase III, US cooperative group trial that compared adjuvant imatinib, for 1 year after primary complete surgical resection, with placebo in primary GIST, reported a significantly shorter time to relapse for those in the placebo group. This led to the approval of imatinib for this new indication in the US and Europe. Several studies evaluating the efficacy of adjuvant imatinib in patients with primary GIST who are at high risk for postoperative relapse are ongoing; in particular two large European studies are expected to yield preliminary results in the near future. Neoadjuvant therapy with imatinib is also being investigated for its effect on surgical outcomes, with first trial results reported.

CONCLUSION

This article provides an update on the rapidly evolving role of surgery, treatment with TKI therapy, and their combination in the management of GIST as well as further reviews pertinent to current clinical research findings.

Hepatitis C and metabolic syndrome

Hepatitis C virus (HCV) and the hepatic manifestation of metabolic syndrome, nonalcoholic fatty liver disease, are the two major causes of chronic liver disease worldwide. Liver histology of both diseases can be associated with steatosis, oxidative stress and fibrogenesis. Although better defined for HCV, approximately 20% of patients with these diseases can also develop cirrhosis or hepatocellular carcinoma. In recent years, it has become clear that the presence of metabolic syndrome and nonalcoholic fatty liver disease negatively impacts HCV-related outcomes, while simultaneously, the progression of HCV may have metabolic consequences in that it encourages or exacerbates insulin resistance. A growing body of evidence suggests that successful treatment of HCV may rely on understanding and addressing the complex and often mutually confounding relationship between HCV and the individual elements that comprise metabolic syndrome.

Complete resection after imatinib treatment of a gastrointestinal stromal tumor of the ileum with peritoneal metastases: report of a case

A 70-year-old woman with a pelvic tumor had undergone exploratory laparoscopy at another institution, which revealed many peritoneal nodules. Immunohistochemical staining of a biopsy specimen of the peritoneal nodules was positive for KIT. Thus, a gastrointestinal stromal tumor (GIST) was diagnosed and imatinib treatment was begun. After 16 months of this treatment, the tumor size had decreased from 51 x 55 mm to 22 x 17 mm, and surgery was performed. Laparotomy revealed complete regression of the peritoneal lesions. The primary tumor was seen to arise from the small intestine and to loosely adhere to the rectum. We performed partial resection of the small intestine. Imatinib therapy was restarted 1 month postoperatively, and the patient is doing well after 12 months of follow-up. We report this case to show that there is the possibility of curative salvage surgery after long-term imatinib treatment in some patients with peritoneal metastases of a GIST.

Imatinib mesylate neoadjuvant treatment for rectal malignant gastrointestinal stromal tumor

Surgical treatments including radical resection and local excision remain the main treatment for primary rectal gastrointestinal stromal tumors (GISTs). However, since patients with high-grade rectal GISTs have a higher risk of tumor recurrence and a shorter life expectancy, neoadjuvant treatment is necessary. In this case report, the efficacy of imatinib mesylate (IM) as a neoadjuvant therapy was assessed in an old man with malignant rectal GIST. The patient received IM preoperative treatment for a short period of one and a half months; at the end of the IM treatment, computed tomography scanning showed a markedly reduced tumor size and cystic changes of the tissue. At that time, a function sphincter-sparing surgery was performed. The histological examination of the resected specimen detected no tumor cells, but residual blood vessels and scattered inflammatory lymphocytes. After surgery, the patient has been followed up without additional IM treatment and remained disease-free for 57 mo. This case indicates that IM neoadjuvant therapy can dramatically improve the prognosis of rectal malignant GIST.

Stage and histological grade of gastrointestinal stromal tumors based on a new approach are strongly associated with clinical behaviors

Tumor stage and grade for gastrointestinal stromal tumors are poorly defined. To develop a better evaluation system, we assessed 12 clinical and pathological parameters in 613 patients with follow-up information. These parameters were classified into two gross spread parameters including liver metastasis and peritoneal dissemination, five microscopic spread parameters including lymph node metastasis, vascular, fat, nerve and mucosal infiltration, and five histological parameters including mitotic count > or =10 per 50 high-power fields, muscularis propria infiltration, coagulative necrosis, perivascular pattern and severe nuclear atypia. The 5-year disease-free survival and overall survival of 293 patients without any of these predictive parameters of malignancy were 99 and 100%, respectively. They were regarded as nonmalignant and further evaluations on the stage and grade of these tumors were not performed. At least one and at most seven predictive parameters of malignancy were identified in 320 patients. For these patients, the 5-year disease-free survival and overall survival rates were 44% (mean 6.7 years) and 60% (mean 9.3 years), respectively. The disease-free survival showed significant difference between patients with and without gross spread (P<0.0001), with and without microscopic spread (P=0.0009). Disease-free survival and overall survival were associated with the number of predictive parameters of malignancy in patients without gross spread (P<0.0001 for both disease-free survival and overall survival), but not in patients with gross spread (P=0.882 and 0.441, respectively). Malignant gastrointestinal stromal tumors could be divided into clinical stage I and II based on the absence and presence of gross spread, respectively. The degree of malignancy of patients in clinical stage I could be graded according to the number of predictive parameters of malignancy. Patients in clinical stage II were of the highest degree of malignancy regardless of the number of parameters. We found that the clinical stage and grade were strongly associated with prognosis.

Analysis of a case with disappearance of the primary gastrointestinal stromal tumor and progressive liver metastases under long-term treatment with tyrosine kinase inhibitors

The response of gastrointestinal stromal tumors (GISTs) to tyrosine kinase receptor inhibitors (TKR-I) has been a breakthrough for small molecular therapy. We report here on the very different long-term outcome of a synchronous metastatic GIST with complete remission of the primary tumor and progressive liver metastases under TKR-I therapy. In 2003, a 52-year-old patient was diagnosed with gastric GIST and synchronous multiple liver metastases. Therapy with imatinib, 400 mg daily, was started immediately. Fifteen months later, the primary was no longer detectable by endoscopy. In 2006, progression of the liver metastases was observed. Mutation analysis of the initial biopsy specimen from the primary, as well as the biopsy from the three main liver metastases after 3 years of imatinib treatment, revealed the common KIT exon 11 deletion (W557_K558del) in all tumor samples. Two of the metastases had a separate secondary mutation in KIT exon 14 and 17, respectively, while the largest cystic metastatic lesion had no other mutation. Imatinib was then increased to a daily dose of 800 mg, and in April 2007 the treatment was changed to sunitinib. Fifty-two months after initial diagnosis, the patient died of liver failure. At no time point, relapse of the gastric primary tumor was observed. Whilst TKR-Is are commonly very effective in treating GISTs, the present case illustrates their varying effects regarding the clinical behavior and genetic variations within different tumors of the same patient after long-term treatment.

Pathologic complete response confirmed by surgical resection for liver metastases of gastrointestinal stromal tumor after treatment with imatinib mesylate

A 39-year-old male underwent distal gastrectomy for a high grade gastrointestinal stromal tumor (GIST). Computed tomography (CT) and magnetic resonance imaging (MRI) 107 mo after the operation, revealed a cystic mass (14 cm in diameter) and a solid mass (9 cm in diameter) in the right and left lobes of the liver, respectively. A biopsy specimen of the solid mass showed a liver metastasis of GIST. The patient received imatinib mesylate (IM) treatment, 400 mg/day orally. Following the IM treatment for a period of 35 mo, the patient underwent partial hepatectomy (S4 + S5). The effect of IM on the metastatic lesions was interpreted as pathologic complete response (CR). Pathologically verified cases showing therapeutic efficacy of IM have been rarely reported.

Interaction of metabolic syndrome, nonalcoholic fatty liver disease and chronic hepatitis C

Nonalcoholic fatty liver disease (NAFLD) has become one of the most prevalent liver diseases in the Western world. NAFLD represents a wide spectrum of histologic subgroups, with nonalcoholic steatohepatitis as the most aggressive form. The risk of developing NAFLD is strongly associated with metabolic syndrome and insulin resistance. The pathogenesis of NAFLD is a multiple-hit process resulting from hepatic fat deposition that is related to several conditions, including insulin resistance and central obesity. Additional hits, such as oxidative stress or adipocytokines produced by white adipose tissue, can further enhance liver damage leading to nonalcoholic steatohepatitis or fibrosis. Although NAFLD is often the primary liver disease of metabolic conditions, it can also exacerbate other liver diseases such as hepatitis C (HCV); indeed, more than 50% of patients with HCV have hepatic steatosis. Hepatic steatosis can be related to host factors (e.g., obesity, metabolic syndrome or insulin resistance) or to the genotype of virus (e.g., HCV genotype 3). Increasing evidence suggests that hepatic steatosis, insulin resistance and obesity in the setting of HCV have a negative impact on the efficacy of treatment and hepatic progression of fibrosis.

Glucose abnormalities are an independent risk factor for nonresponse to antiviral treatment in chronic hepatitis C

OBJECTIVES

The influence of glucose abnormalities on the efficacy of antiviral treatment is unknown. This study investigated whether glucose abnormalities (impaired fasting glucose and type 2 diabetes) influence the response to antiviral therapy with interferon plus ribavirin in patients with chronic hepatitis C.

METHODS

A total of 178 treatment-naïve patients with chronic hepatitis C treated with combination therapy were retrospectively studied. SVR was assessed after completing treatment. Fasting plasmatic glucose was measured prior to therapy.

RESULTS

Compared with nonresponders (N = 111), patients with SVR (N = 67) had lower plasma glucose (94.1 +/- 12.7 vs 104.4 +/- 25.8 mg/dL, P= 0.001) and a lower prevalence of glucose abnormalities (24.24%vs 44.14%, P= 0.012). The SVR rate was 45.13% in patients with normoglycemia (N = 113), 28.26% in patients with impaired fasting glucose (N = 46), and 15.78% in type 2 diabetic patients (N = 19) (P < 0.001). Multivariate logistic regression identified genotype 1 (OR 1.55, 95% CI 1.01-2.41, P= 0.05), gamma-glutamyltranspeptidase level (OR 6.41, 95% CI 1.86-22.07, P= 0.003), and presence of glucose abnormalities (OR 2.33, 95% CI 1.04-5.20, P= 0.039) as being independently associated with the absence of an SVR. In addition, patients with glucose abnormalities (N = 65) showed a lower virological response rate when compared with a subgroup of normoglycemic patients (N = 65) matched for sex, age, and liver fibrosis (24.6%vs 44.6%, P= 0.001).

CONCLUSIONS

Glucose abnormalities are an independent predictor of poor virological response to combined therapy in hepatitis C virus infected patients.

The challenge of opportunities: how far can and should we go with targeted treatments and modern diagnostics in gastrointestinal stromal tumors?

The introduction of imatinib has greatly improved the treatment options and quality of life of patients with gastrointestinal stromal tumors. Systemic treatment with imatinib alone most likely, however, does not cure the disease because, despite long-lasting major remissions, the majority of patients eventually relapse. Therefore, complete surgical resection remains the only curative approach in patients with gastrointestinal stromal tumors. Given a strong systemic treatment option at hand, the use of multimodal treatment strategies for patients with locally advanced or metastatic disease seems self-evident as many tumors become resectable after a treatment with imatinib. Few retrospective and no prospective data, however, are yet available on feasibility and the prognostic impact of these strategies, which represents a major challenge on how to decide on these patients in clinical practice. We therefore critically discuss the available evidence and current concepts for multimodal treatment of gastrointestinal stromal tumors and how modern diagnostics, such as KIT genotyping, may influence our clinical decision-making in this context.

Surgical management after neoadjuvant imatinib therapy in gastrointestinal stromal tumours (GISTs) with respect to imatinib resistance caused by secondary KIT mutations

BACKGROUND

In metastasized GISTs, resistance to imatinib after initial tumour response has been associated with observation of secondary mutations in the activation loop of KIT. The aim of the current study was to evaluate the tumour response and observance of secondary KIT mutations in a case of GIST undergoing neoadjuvant imatinib therapy.

METHODS

We report on a case of an initially unresectable gastric GIST with curative resection after 10 months of neoadjuvant imatinib therapy. Mutation analysis of KIT was performed on a pretherapeutic biopsy specimen, as well as on the resected tumour specimen.

RESULTS

The pretherapeutic biopsy revealed cKit positive tumour cells with mutation of KIT exon 11 Del 560-576. The remaining tumour mass after neoadjuvant imatinib therapy almost exclusively consisted of hypocellular myxohyalinale stroma with rare microfoci of cKit positive tumour cells. Laser microdissection of several tumour microfoci revealed two additional point mutations located in the activation loop of KIT exon 17, C809G and N822Y, each observed separately in a distinct microfocus. Neither of these two point mutations has been reported in a GIST so far.

CONCLUSIONS

Neoadjuvant imatinib therapy successfully reduces tumour size in GISTs. Since resistance relevant secondary mutations of the activation loop of KIT may be observed after neoadjuvant imatinib therapy, the time elapse with preoperative imatinib therapy should be chosen as short as curative tumour resection or function sparing surgery can be carried out. The determination of the optimal time point for surgery is therefore a critical event and will be discussed.