Pembrolizumab: Groundbreaking Immunotherapy Trial Shows Promise for Bowel Cancer Treatment


Recent clinical trial results have revealed that an immunotherapy drug administered before surgery instead of chemotherapy significantly improved outcomes for patients with a specific genetic profile of bowel cancer. The findings, presented at the American Society of Clinical Oncology (ASCO) Annual Meeting 2024, showcase the interim results from the NEOPRISM-CRC phase II clinical trial. This trial assesses whether pembrolizumab, an immunotherapy drug, can enhance the prognosis for patients with stage 2 or stage 3 MMR deficient/MSI-High bowel cancer. This document provides an in-depth analysis of the trial, its outcomes, and its potential implications for the future of bowel cancer treatment.

Background on Bowel Cancer

Bowel cancer, also known as colorectal cancer, is the fourth most common cancer in the UK, with approximately 42,900 new cases diagnosed annually. Although predominantly affecting older adults, the incidence among individuals under 50 has been rising in recent decades. Early detection of bowel cancer significantly increases the likelihood of successful treatment. For instance, the five-year survival rate for stage 1 bowel cancer is over 90%. However, survival rates drop dramatically for more advanced stages, with stage 3 and stage 4 bowel cancers having five-year survival rates of 65% and 10%, respectively.

The NEOPRISM-CRC Phase II Clinical Trial

Objectives and Design

The NEOPRISM-CRC trial aims to evaluate the efficacy of pembrolizumab as a pre-surgical treatment for patients with stage 2 or stage 3 MMR deficient/MSI-High bowel cancer. Pembrolizumab is an immune checkpoint inhibitor that works by preventing cancer cells from suppressing the immune system, thereby allowing the body’s immune response to target and destroy the cancer cells.

Patient Recruitment and Treatment Protocol

Researchers from University College London (UCL) recruited 32 patients with the specified genetic profile from five hospitals across the UK. This genetic makeup is present in approximately 10-15% of stage 2 or stage 3 bowel cancer cases, translating to around 2,000-3,000 cases per year in the UK. Patients received nine weeks of pembrolizumab before undergoing surgery, deviating from the conventional treatment of chemotherapy followed by surgery.

Interim Results

The interim results presented at the ASCO Annual Meeting 2024 are promising. The key findings include:

  • 59% of patients showed no signs of cancer after pembrolizumab treatment.
  • The remaining 41% had their cancer completely removed during surgery.
  • All patients were cancer-free after treatment and remained so for several months post-treatment, with a median cancer-free period of 9.7 months (ranging from 5.3 to 19 months).
  • Conventional chemotherapy results in less than 5% of patients with this genetic profile being cancer-free after surgery.

Patient Experiences and Testimonials

Patients who participated in the trial reported positive outcomes and minimal side effects from the treatment. For instance, Darren Evans, a 47-year-old participant, described how the immunotherapy shrunk his tumor from the size of a golf ball to nearly nothing, facilitating a more straightforward surgical removal.

Eileen Unsworth, a 77-year-old patient, shared her experience of feeling revitalized after each immunotherapy session and successfully undergoing surgery with minimal remaining tumor tissue.

Detailed Analysis of Pembrolizumab and Its Mechanism

Immunotherapy and Pembrolizumab

Immunotherapy harnesses the body’s immune system to fight cancer. Pembrolizumab, specifically, is an immune checkpoint inhibitor that targets the PD-1 pathway. By blocking the interaction between PD-1 on T cells and its ligands PD-L1 and PD-L2 on cancer cells, pembrolizumab prevents the suppression of the immune response, enabling T cells to effectively attack cancer cells.

Clinical Applications and Approval Status

Pembrolizumab has been approved for use in the UK for various cancers, including breast cancer, melanoma, cervical cancer, and certain types of lymphomas and carcinomas. Its success in these cancers has paved the way for exploring its efficacy in treating bowel cancer.

Safety and Efficacy

The trial results indicate that pembrolizumab is both safe and effective for patients with high-risk bowel cancers. The significant reduction in tumor size and the high percentage of cancer-free outcomes post-treatment highlight its potential as a game-changing treatment option.

Comparative Analysis: Pembrolizumab vs. Conventional Chemotherapy


Compared to conventional chemotherapy, pembrolizumab shows a significantly higher success rate in eliminating cancer cells pre-surgery. While less than 5% of patients treated with standard chemotherapy remain cancer-free after surgery, 59% of those treated with pembrolizumab showed no signs of cancer before surgery.

Side Effects

Chemotherapy is associated with a range of severe side effects, including nausea, fatigue, and increased susceptibility to infections. In contrast, patients treated with pembrolizumab reported minimal side effects, improving their overall quality of life during treatment.

Long-term Outcomes

While the interim results are promising, long-term data on survival and relapse rates are still being collected. However, the initial indications suggest that pembrolizumab could lead to better long-term outcomes compared to conventional treatments.

Implications for Future Treatment Protocols

Potential to Replace Chemotherapy

The success of pembrolizumab in the NEOPRISM-CRC trial suggests that it could potentially replace chemotherapy as the standard pre-surgical treatment for patients with MMR deficient/MSI-High bowel cancer. This shift would not only improve patient outcomes but also reduce the burden of chemotherapy-related side effects.

Expansion to Other Cancer Types

Given pembrolizumab’s efficacy in various cancers, its use could be expanded to other cancer types with similar genetic profiles. Ongoing and future clinical trials will help determine its broader applicability.

Integration into Standard Care

The integration of pembrolizumab into standard care protocols will require collaboration between oncologists, surgeons, and researchers. Training and resources will be necessary to ensure that healthcare providers are equipped to administer and monitor this treatment effectively.

Support and Collaboration

Funding and Sponsorship

The NEOPRISM-CRC trial is funded by Merck Sharp and Dohme and conducted by the CRUK & UCL Cancer Trials Centre. This collaboration underscores the importance of pharmaceutical and research partnerships in advancing cancer treatment.

Role of Clinical and Research Infrastructure

The trial benefits from the support of the National Institute for Health and Care Research (NIHR) through the UCLH Biomedical Research Centre (BRC) and Clinical Research Facility (CRF). These facilities provide the necessary infrastructure for conducting high-quality clinical trials.

Patient Advocacy and Participation

Importance of Clinical Trials

Clinical trials play a crucial role in developing new treatments and improving patient outcomes. Patient participation is vital for the success of these trials, as highlighted by the experiences of trial participants like Darren Evans and Eileen Unsworth.

Encouraging Participation

Efforts should be made to encourage more patients to participate in clinical trials. This includes providing comprehensive information about the trials, addressing potential concerns, and highlighting the potential benefits of participation.


The interim results of the NEOPRISM-CRC phase II clinical trial suggest that pembrolizumab is a highly effective treatment for patients with MMR deficient/MSI-High bowel cancer. This immunotherapy drug has shown a remarkable ability to reduce tumor size and improve patient outcomes with minimal side effects. As more data becomes available, pembrolizumab could revolutionize the treatment protocol for this type of bowel cancer, offering hope to thousands of patients each year. Continued research and collaboration will be essential to confirm these findings and integrate this promising treatment into standard care practices.

References and Further Reading

  1. American Society of Clinical Oncology (ASCO) Annual Meeting 2024 Proceedings.
  2. UCL Cancer Institute Publications.
  3. National Institute for Health and Care Research (NIHR) Reports.
  4. Clinical trial database: NCT05197322 (NEOPRISM-CRC).

By comprehensively analyzing the interim results of the NEOPRISM-CRC trial, this document provides a detailed overview of the potential of pembrolizumab as a groundbreaking treatment for bowel cancer. Continued research and collaboration will be essential to fully realize the benefits of this promising approach.


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