FAPI Molecular Imaging for Diagnosis of the CMS4 Unfavorable Colorectal Cancer Subtype

Summary

Colorectal cancer (CRC) is the 3rd most common cancer worldwide and accounts for \~14,000 new diagnoses and \~5,000 deaths in the Netherlands yearly (1.9 million and 935 thousand on a global level). Large scale transcriptional profiling of primary CRC tumors has revealed the presence of four distinct consensus molecular subtypes (CMSs). The CMS4 subtype is associated with a poor prognosis, especially in early CRC, and may benefit less from several standard systemic treatments (e.g. oxaliplatin, 5-fluorouracil, cetuximab), while being relatively sensitive to irinotecan. This is relevant as in the metastatic setting often the first choice first-line systemic therapy regimen is oxaliplatin and not irinotecan-based. Furthermore, tumor cells can acquire a CMS4 phenotype following exposure to chemotherapy, which may contribute to therapy resistance. CMS4 accounts for \~25% of all early-stage CRC patients and is more prevalent in advanced disease stages (\~40% in stage IV CRC). Currently available CMS4 diagnostic tests require tumor tissue samples. The interpretation of biopsy-based CMS4 diagnosis is however complicated by large intra- and inter-lesion heterogeneity of CMS4 status. Extensive biopsy protocols could address the problem of CMS4 heterogeneity but are challenging in routine clinical practice. The development of CMS4-targeted therapy strategies therefore requires a more robust and clinically applicable diagnostic test for comprehensive quantitative assessment of CMS4 status of all lesions - primary and metastatic - in individual cancer patients. A promising solution for such a diagnostic test is to use a radiotracer that enables the quantitative assessment of CMS4 in vivo by whole body molecular imaging. This technique is particularly suited to assess biomarkers with heterogeneous expression: for diagnostic purposes, as a companion diagnostic for (targeted) therapies, or as part of a 'theranostic' strategy where patient selection using the diagnostic radiotracer is followed by treatment with the same tracer labeled to a therapeutic compound. Radiolabeled fibroblast activating protein inhibitor (FAPI) is an emerging diagnostic radiotracer that allows the comprehensive whole-body, whole-tumor assessment of fibroblast activation protein (FAP) expression in humans with a very low background uptake also at frequent CRC metastatic sites including the liver. FAP is an excellent candidate molecular imaging target for CMS4, as it is highly expressed on cancer-associated fibroblasts (CAF) that are abundantly present in this CRC subtype. Indeed, the investigators found that FAP gene-expression measured in tumor biopsies - as a single marker - accurately discriminates CMS4 from other CRC subtypes (area under the receiver operating characteristic curve (AUROC): 0.91; 95% confidence interval (CI): 0.90-0.93). The FoCus study will aim to take a next step by relating in vivo assessed FAP protein-expression by \[18F\]-ALF-FAPI-74 positron emission tomography (PET) / computed tomography (CT) to CMS4 status in patients eligible for colorectal liver metastatectomy as a first proof of concept. Ultimately this will contribute to the development of a diagnostic tool for the comprehensive assessment of CMS4 load in patients with (metastatic) CRC by using \[18F\]-ALF-FAPI-74 PET/CT molecular imaging, to guide CMS4 subtype-directed therapy decisions.

Eligibility

Inclusion Criteria:

* Age ≥ 18 years.
* Candidates for liver metastatectomy at the time of liver metastasis diagnosis as clinically indicated in the tumor board (RAKU).
* Patients must have given written informed consent.
* At least one liver metastasis should have a longest diameter of a least 1.5 cm as measured on routinely performed imaging (e.g. magnetic resonance imaging, CT-scan or ultrasound). This minimum diameter will guarantee sufficient tissue material for analysis and will prevent underestimation of \[18F\]-ALF-FAPI-74 uptake due to partial volume effects.
* CRC patients who received prior treatment before clinical indication for surgical liver metastases resection (both synchronous and metachronous patients, as well as a re-resection of liver metastatic disease) are allowed to enter the study. This is because our prime interest is in the relation between FAPI uptake and the presence of CMS4 at the same point in time, which will likely not be biased by earlier therapies.
* It is allowed for patients to receive concurrent radiofrequency ablation or other local treatments directed to other metastatic disease locations, if at least one liver metastasis of sufficient size is planned to be surgically removed and therefore available for tissue analysis.
* It is allowed for patients to be treated with pre-surgical radiotherapy directed to the primary tumor (e.g. in rectal cancer patients).

Exclusion Criteria:

* Pregnancy.
* Patients treated with a pre-surgical chemotherapy regimen that does not include a fluoropyrimidine.

Conditions5

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