A significant challenge in assessing complete response after neoadjuvant immunotherapy for rectal cancer is the presence of mucin pools. These imaging abnormalities can persist for up to two years, mimicking residual tumor and complicating decisions about non-operative management.

Sentinel lymph node biopsy was historically inconsistent in CSCC because a positive finding had no approved systemic treatment path. With adjuvant cemiplimab's approval, identifying microscopic nodal disease now directly impacts treatment eligibility, potentially making the procedure a new standard of care for certain high-risk patients.

While neoadjuvant immunotherapy shows astounding success in MSI-high rectal cancer, the primary difficulty for clinicians lies in accurately assessing complete response via endoscopy and MRI, and managing unique complications like mucin pools or stenosis, rather than simply administering the treatment.

Historically, discussing adjuvant therapy for Stage III colon cancer was quick and straightforward, while Stage II was complex. The advent of ctDNA testing has reversed this dynamic. Stage II decisions are now clearer (treat if positive), while Stage III discussions have become much longer and more nuanced as clinicians integrate ctDNA data with patient preferences.

With 72% response rates to neoadjuvant immunotherapy, surgeons are shifting from immediate, aggressive surgery to a "wait-and-see" approach. Shrinking the tumor first can turn a morbid, disfiguring operation into a much simpler procedure, fundamentally changing the initial surgical evaluation for cutaneous squamous cell carcinoma (CSCC).

While the ATOMIC trial established FOLFOX plus atezolizumab as a new standard for adjuvant therapy in MSI-high colon cancer, its design lacked an immunotherapy-only arm. This leaves a critical, unanswered question about the actual contribution and necessity of the chemotherapy component.

After immunotherapy, many colorectal cancer patients have residual nodules on scans that appear to be partial responses. However, ctDNA testing can confirm these are often just scar tissue, not active disease. This provides the confidence to stop therapy at the two-year mark and avoid unnecessary surgeries for what are effectively complete responses.

A potential complication of successful neoadjuvant immunotherapy in rectal cancer is the development of stenosing scar tissue. This can block the lumen, making endoscopic surveillance impossible and necessitating surgery for a patient who may have otherwise achieved a complete clinical response.

Dr. Radvanyi advocates for a paradigm shift: treating almost all cancers with neoadjuvant immunotherapy immediately after diagnosis. This "kickstarts" an immune response before standard treatments like surgery and chemotherapy, which are known to be immunosuppressive, can weaken the patient's natural defenses against the tumor.