2026-03-10
Colorectal cancer: why do treatments stop working?
Oncology
By Ana Espino | Published on March 10, 2026 | 3 min read
Colorectal cancer (CRC) remains one of the leading causes of cancer-related mortality worldwide, despite major advances in surgery, chemotherapy, and targeted therapies. Improvements in diagnostic strategies and the introduction of modern therapeutic combinations have increased survival, particularly in metastatic disease. However, these gains are undermined by the almost inevitable emergence of therapeutic resistance, which leads to relapse and tumor progression.
Standard treatment protocols combine cytotoxic agents such as 5-fluorouracil, oxaliplatin, and irinotecan with targeted therapies directed against EGFR or VEGF. More recently, immunotherapy has shown efficacy in subgroups of patients with high microsatellite instability. Nevertheless, a significant proportion of patients exhibit primary resistance, while others develop acquired resistance after an initial response.
This resistance does not arise from a single mechanism but from a complex interaction between genetic alterations, tumor plasticity, the immune microenvironment, and therapeutic pressure. Understanding these mechanisms has become essential for optimizing treatment personalization and extending survival. This review, published in 2025 in the International Journal of Molecular Sciences, provides an in-depth analysis of the molecular and cellular mechanisms involved in therapeutic resistance in CRC, as well as innovative strategies aimed at preventing or overcoming it.
This review summarizes the mechanisms underlying resistance to chemotherapy, targeted therapies, and immunotherapy.
At the molecular level, mutations in KRAS, NRAS, or BRAF alter the response to EGFR inhibitors. Constitutive activation of the MAPK and PI3K/AKT pathways promotes cellular proliferation independent of therapeutic signals. Alterations in the TP53 gene reduce apoptosis induction following exposure to cytotoxic agents.
Resistance to oxaliplatin and irinotecan involves enhanced DNA repair mechanisms, overexpression of efflux transporters such as P-glycoprotein, and metabolic reprogramming. Cancer stem cells also contribute to clonal persistence following treatment.
The tumor microenvironment plays a crucial role. Hypoxia, chronic inflammation, and interactions with cancer-associated fibroblasts promote tumor cell survival. In addition, resistance to immunotherapy is often linked to microsatellite stability (MSS), which limits the effectiveness of immune checkpoint inhibitors.
The authors describe several strategies to overcome these resistances. These include therapeutic combinations targeting multiple signaling pathways simultaneously, BRAF inhibitors combined with anti-EGFR agents, modulation of the tumor microenvironment, and the development of predictive biomarkers to personalize treatment.
Therapeutic resistance represents one of the major barriers to durable survival improvement in colorectal cancer.
This review aimed to decipher the underlying biological mechanisms and identify strategies to overcome them. The data indicate that resistance results from complex interactions between genetic alterations, tumor plasticity, and the tumor microenvironment, highlighting the need for a multidimensional approach.
Current limitations include significant inter- and intra-tumor heterogeneity, which makes it difficult to accurately predict resistance mechanisms. Moreover, the clinical validation of combination strategies requires robust prospective trials.
In the long term, integrating molecular biomarkers, multi-omics analyses, and adaptive therapeutic strategies may allow clinicians to anticipate and overcome resistance, paving the way for a more personalized and dynamic approach to colorectal cancer treatment.
About the author – Ana Espino
PhD in Immunology, specialized in Virology
As a scientific writer, Ana is passionate about bridging the gap between research and real-world impact. With expertise in immunology, virology, oncology, and clinical studies, she makes complex science clear and accessible. Her mission: to accelerate knowledge sharing and empower evidence-based decisions through impactful communication.
Colorectal cancer (CRC) remains one of the leading causes of cancer-related mortality worldwide, despite major advances in surgery, chemotherapy, and targeted therapies. Improvements in diagnostic strategies and the introduction of modern therapeutic combinations have increased survival, particularly in metastatic disease. However, these gains are undermined by the almost inevitable emergence of therapeutic resistance, which leads to relapse and tumor progression.
Standard treatment protocols combine cytotoxic agents such as 5-fluorouracil, oxaliplatin, and irinotecan with targeted therapies directed against EGFR or VEGF. More recently, immunotherapy has shown efficacy in subgroups of patients with high microsatellite instability. Nevertheless, a significant proportion of patients exhibit primary resistance, while others develop acquired resistance after an initial response.
This resistance does not arise from a single mechanism but from a complex interaction between genetic alterations, tumor plasticity, the immune microenvironment, and therapeutic pressure. Understanding these mechanisms has become essential for optimizing treatment personalization and extending survival. This review, published in 2025 in the International Journal of Molecular Sciences, provides an in-depth analysis of the molecular and cellular mechanisms involved in therapeutic resistance in CRC, as well as innovative strategies aimed at preventing or overcoming it.
How does the tumor evade treatment?
This review summarizes the mechanisms underlying resistance to chemotherapy, targeted therapies, and immunotherapy.
At the molecular level, mutations in KRAS, NRAS, or BRAF alter the response to EGFR inhibitors. Constitutive activation of the MAPK and PI3K/AKT pathways promotes cellular proliferation independent of therapeutic signals. Alterations in the TP53 gene reduce apoptosis induction following exposure to cytotoxic agents.
Resistance to oxaliplatin and irinotecan involves enhanced DNA repair mechanisms, overexpression of efflux transporters such as P-glycoprotein, and metabolic reprogramming. Cancer stem cells also contribute to clonal persistence following treatment.
The tumor microenvironment plays a crucial role. Hypoxia, chronic inflammation, and interactions with cancer-associated fibroblasts promote tumor cell survival. In addition, resistance to immunotherapy is often linked to microsatellite stability (MSS), which limits the effectiveness of immune checkpoint inhibitors.
The authors describe several strategies to overcome these resistances. These include therapeutic combinations targeting multiple signaling pathways simultaneously, BRAF inhibitors combined with anti-EGFR agents, modulation of the tumor microenvironment, and the development of predictive biomarkers to personalize treatment.
Anticipating resistance to improve treatment
Therapeutic resistance represents one of the major barriers to durable survival improvement in colorectal cancer.
This review aimed to decipher the underlying biological mechanisms and identify strategies to overcome them. The data indicate that resistance results from complex interactions between genetic alterations, tumor plasticity, and the tumor microenvironment, highlighting the need for a multidimensional approach.
Current limitations include significant inter- and intra-tumor heterogeneity, which makes it difficult to accurately predict resistance mechanisms. Moreover, the clinical validation of combination strategies requires robust prospective trials.
In the long term, integrating molecular biomarkers, multi-omics analyses, and adaptive therapeutic strategies may allow clinicians to anticipate and overcome resistance, paving the way for a more personalized and dynamic approach to colorectal cancer treatment.
Read next: Colorectal cancer: a hidden intestinal virus may double the risk
About the author – Ana Espino
PhD in Immunology, specialized in Virology
As a scientific writer, Ana is passionate about bridging the gap between research and real-world impact. With expertise in immunology, virology, oncology, and clinical studies, she makes complex science clear and accessible. Her mission: to accelerate knowledge sharing and empower evidence-based decisions through impactful communication.
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