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Case history

image A 59-year-old man presented with acute-onset severe chest pain and dyspnoea, associated with hypoxia and atrial arrhythmias. He had no other significant comorbidities and was a non-smoker. A plain chest radiograph revealed a retrocardiac mass. A CT pulmonary angiogram (Figure 6.1) was performed to exclude a pulmonary embolus. This demonstrated a significant (17.6 cm × 8.8 cm) heterogeneous enhancing mass, which occupied the greater part of the posterior mediastinum, displacing the lungs laterally, compressing the lower lobes and significantly impinging on the posterior surface of the pericardium and heart. The mass appeared to arise alongside the lower third of the oesophagus. There was no radiological evidence of locoregional lymphadenopathy or metastatic disease.

An endoscopic ultrasound-guided biopsy of the posterior mediastinal mass demonstrated morphological features consistent with a gastrointestinal stromal tumour (GIST). Immunohistochemistry revealed strong expression of c-Kit and DOG-1 (discovered on GIST-1), but was negative for smooth muscle actin, desmin and S100 protein. There was insufficient material to perform KIT mutation analysis.

A staging PET CT scan confirmed a posterior mediastinal tumour with marked fluorodeoxyglucose (FDG) uptake largely around the periphery. At its inferior extent, the tumour was seen to widen the oesophageal diaphragmatic hiatus and was indistinguishable from the oesophagus. There was no evidence of metastatic disease.

The mass was deemed unresectable by virtue of its size and the patient commenced neoadjuvant imatinib 400 mg daily. An early interval PET CT scan after 6 weeks of treatment demonstrated a marked reduction in metabolic activity in the posterior mediastinal mass in keeping with an excellent response to treatment. He continued neoadjuvant imatinib for 13 months, achieving a good partial response (Figure 6.2).

Following maximal tumour response, the patient underwent an oesophagectomy and resection of the intact residual mass including adherent pericardium and a segment of the right lower lobe. Postoperative histology revealed an R0 resection with evidence of complete pathological response. Thereafter, he completed a further 2 years of adjuvant imatinib treatment. He remains well with no evidence of disease recurrence 18 months after discontinuing imatinib.

How is the diagnosis of GIST made?

What was the aim of treatment for this patient?

Why is imatinib such an effective treatment for GISTs?

How does mutation analysis help to determine the appropriate management of patients with locally advanced GIST?

What is the evidence base for his treatment?

Figure 6.1

Baseline CT chest performed at presentation showing a huge posterior mediastinal mass arising alongside the lower third of the oesophagus, displacing and compressing the heart and lungs.

Figure 6.2

Follow-up CT chest performed after 12 months of neoadjuvant imatinib, demonstrating a significant reduction in the size of the posterior mediastinal mass.

How is the diagnosis of GIST made?

GISTs are the most common ...

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