The Value of PET / MRI for the Assessment of Lymph Node Metastasis and Other Prognostic Factors in Patients With Rectal Cancer

Today, there is a variety of treatment options in diagnosed rectal cancer. The standard treatment is surgery with removal of the tumour including surrounding fat and lymph nodes in a package. Prior to surgery, the patient may be given a shorter or longer radiation treatment, the latter in combination with cytostatics, depending on staging at the time of diagnosis. Cytostatic drugs can also be given post surgery. The choice of treatment for the individual patient is based on the assessment of the imaging, ie conventional X-ray, ultrasound, computed tomography, (CT), Magnet Resonance Tomography Imaging (MRI) and Positron Emission Tomography in combination with CT (PET/CT). An accurate staging assessment is crucial for adequate treatment of rectal cancer patients to avoid over treatment, which in itself causes unnecessary suffering, or under treatment with increased risk of relapse. With today's methods, tumor size, overgrowth of other organs and spread to other organs such as liver and lung can be reasonable assessed. On the other hand, there is great uncertainty when assessing spread to lymph nodes. Better safety is also needed for other prognostically important factors such as tumor involvement of the mesorectal fasciae (MRF), i.e. the rectum surrounding the tumor, and tumor growth in venous vessels outside the intramural invasion of the intestinal wall, EMVI.

Hybrid imaging with PET combined with magnetic resonance imaging (PET/MR) is a novel method and there are currently no published studies comparing the outcome of fluoro-deoxy glucose (FDG) -PET/MR with CT, MR, PET/CT at staging of rectal cancer, both primarily and after radiation and cytostatics treatment (CRT). In this study, the investigator plan to evaluate the additional value for PET/MR in rectal cancer. Only patients to be operated are included and microscopic examination of the preparation, histopathology, will be the reference method with which survey data from the imaging methods are compared. The investigator also want to evaluate the relationship between the radiological findings and biomarkers in blood and tumor tissue to determine if there is a relationship that can provide additional prognostic information. The investigator will only include patients with intermediate and high-risk rectal cancer, as low-risk cancer is unusual with spread to lymph nodes. The study will be a prospective observation study in which all consecutive elective patients in Umeå with confirmed intermediate and high risk type rectal cancer, which give their consent, are included and examined preoperatively. Thereafter, imaging and blood and tumor tissue samples are examined and evaluated.

Primary research questions:

• Can FDG-PET/MR provide improved accuracy in assessment of local tumor proliferation, lymph node metastasis and other important prognostic factors (MRF +, EMVI) in rectal cancer compared to currently used methods magnetic resonance imaging, (MRI), PET/CT or CT?
• Can FDG-PET/MR provide an improved accuracy in assessment of tumor regression following combined cytostatics and radiotherapy in rectal cancer compared to MRI or PET/CT?
• Can FDG-PET / MR in combination with blood and tumor tissue biomarkers provide additional prognostic information for intermediate and high-risk rectal cancer?

Secondary research questions: