[Hyperprogression in a patient with colorectal cancer and repair protein deficiency: a diagnostic and therapeutic challenge].

Metastatic colorectal cancer (mCRC) represents a significant global public health challenge. The identification of biomarkers such as microsatellite instability (MSI) and the status of mismatch repair (MMR) proteins, among others, provides crucial information for guiding therapeutic decisions and predicting prognosis. Immune checkpoint inhibitors (ICIs) are the treatment of choice for patients with deficient MMR (dMMR) or high microsatellite instability (MSI-H). The assessment of treatment response using iRECIST highlights two new patterns: pseudoprogression and hyperprogression (HP). The latter is characterized by rapid clinical deterioration and a doubling of tumor burden within less than two months. In this article, we present, which, to our knowledge, is the first reported case in the literature of a patient with mCRC who developed HP after receiving nivolumab/ipilimumab treatment. Although various hypotheses have been proposed to explain this phenomenon, no clear predictive factors have been identified to date. Prospective studies are needed to anticipate the development of this entity and thereby optimize patient selection.