Case report: Efficacy of immunotherapy as conversion therapy in dMMR/MSI-H colorectal cancer: a case series and review of the literature.

Immunotherapy has demonstrated a role in the therapeutic landscape of a small subset of patients with colorectal carcinoma (CRC) that harbor a microsatellite instability (MSI-H) status due to a deficient DNA mismatch repair (dMMR) system. The remarkable responses to immune checkpoint inhibitors (ICIs) are now being tested in the neoadjuvant setting in localized CRC, where the dMMR/MSI-H status can be found in up to 15% of patients, with remarkable results obtained in NICHE2 and 3 trials, among others. This case series aims to report our experience at a tertiary center and provide a comprehensive analysis of the possible questions and challenges to overcome if ICIs were established as standard of care in a neoadjuvant setting, as well as the potential role they may have as conversion therapy not only in locoregional advanced CRC but also in oligometastatic disease.

Current Landscape and Potential Challenges of Immune Checkpoint Inhibitors in Microsatellite Stable Metastatic Colorectal Carcinoma.

Colorectal cancer (CRC) is the third most frequent cancer and the second most common cause of cancer-related death in Europe. High microsatellite instability (MSI-H) due to a deficient DNA mismatch repair (dMMR) system can be found in 5% of metastatic CRC (mCRC) and has been established as a biomarker of response to immunotherapy in these tumors. Therefore, immune checkpoint inhibitors (ICIs) in mCRC with these characteristics were evaluated with results showing remarkable response rates and durations of response. The majority of mCRC cases have high levels of DNA mismatch repair proteins (pMMR) with consequent microsatellite stability or low instability (MSS or MSI-low), associated with an inherent resistance to ICIs. This review aims to provide a comprehensive analysis of the possible approaches to overcome the mechanisms of resistance and evaluates potential biomarkers to establish the role of ICIs in pMMR/MSS/MSI-L (MSS) mCRC.

Resistance to RET targeted therapy in Thyroid Cancer: Molecular basis and overcoming strategies.

Thyroid cancer is the most frequently diagnosed endocrine malignancy, with an increasing incidence over the last decades. The recent advances in understanding the molecular mechanisms underlying the carcinogenesis of thyroid cancer have led to a better therapeutic approach of these tumors. This has allowed the development and approval of several drugs during the past decade. The rearranged during transfection [RET] protooncogene encodes a transmembrane receptor tyrosine kinase, which is activated by chromosomal rearrangements or point mutations in multiple malignancies, including thyroid cancer. Selective RET inhibitors have proved their value in the treatment algorithm in molecularly selected patients with significantly high response rates and duration of response. Notwithstanding, there are patients who experiment rapid progression or tumor recurrence after an early response to those targeted therapies, which suggest the existence of primary and acquired mechanisms of resistance that have been largely unknown to date. In the present review, we attempt to provide a comprehensive analysis of the most relevant mechanisms of resistance to RET inhibitors which could help in the development of next generation MKI and RET inhibitors, along with combination strategies with different targeted therapies that could potentially overcome these resistances.