Rationale: Current standard treatment of localized esophageal cancer (EC) with neoadjuvant chemoradiotherapy (nCRT) followed by esophagectomy with curative intent results in 30% complete, 40-60% partial and 20% no-response at pathologic examination. Clinical response of nCRT is usually evaluated with PET-CT. However, response measurements are currently still insufficient in optimizing EC treatment. Proper pre-surgical response prediction may allow individualized treatment with esophagus-preservation in complete responders or switching to an alternative treatment in non-responders. Interestingly, in many tumors, a subset of cells has been found to possess cancer stem cell (CSC) properties with associated signaling as drivers of tumor (re-)growth and therapy resistance. Response of CSC-derived tissue resembling in vitro cultured tumor organoids may reflect patient's tumors sensitivity to therapy.

Objective: To create a patient derived organoid model for EC patients to predict the pathologic tumor response to nCRT in clinical practice. This will allow a more personalized approach in future treatment of locally advanced EC.

Study design: Fresh esophageal tumor material will be collected during diagnostic endoscopic ultrasound (EUS) in participating patients. These biopsies will be used to select cancer stem cells, which will be cultured to derive organoids (esophageal cancer patient derived organoids; EC-PDO). When the EC-PDO contain sufficient cells, these cells will be treated with radiotherapy and/or chemotherapy in order to obtain dose-response curves. The response of these EC-PDOs will be compared to the actual tumor response to nCRT treatment in these EC patients, which will be assessed at the definitive pathologic examination of the resection specimen after esophagectomy with curative intent.

Study population: All patients with curatively treatable and resectable esophageal cancer (adenocarcinoma or squamous cell carcinoma) can be included in this trial.

Main study parameters/endpoints: The main endpoint is response prediction to chemoradiotherapy by EC-PDO; the steepness of the dose response survival curve in the organoids in relation to the pathologic response after resection in the clinical situation.

Nature and extent of the burden and risks associated with participation, benefit and group relatedness: The patients will be asked to undergo 3 to 6 additional biopsies during endoscopic ultrasonography (EUS) for the TNM staging of the tumor. The risk of these additional biopsies is not greater than the biopsies for the diagnosis of EC. The patient will not benefit from participation in this trial.

For the future approach we can get more insight into the mechanism of (chemo)radiation response or resistance to nCRT, which might lead to a better patient selection and more individualized esophageal cancer treatment in the future. This improvement in selection and treatment can result in less over or under-treatment of these EC patients.

Inclusion Criteria:

• Histologically proven adeno- or squamous cell carcinoma of the esophagus
• Age ≥ 18 years
• Candidates for curative treatment; clinical stage T1N+/T2-4aN0-3M0
• Scheduled for endoscopic ultrasound (EUS) procedure for staging and/or treatment purposes
• Written informed consent

Exclusion Criteria:

• Patients who are medically unfit for a curative treatment
• Signs of distant metastases (M1)
• Patients who are mentally disabled or incapable to give informed consent

All patients with histologically proven adenocarcinoma or squamous cell carcinoma of the esophagus, who are candidates for nCRT followed by resection, can be included in this trial.