Despite improved survival rates, colorectal cancer is the third leading cause of cancer-related deaths in the U.S. Though rates of colorectal cancer have declined among people 65 and older, largely thanks to increased screening efforts, rates among younger adults are rising. When the cancer is caught early, many patients can remain disease-free for the rest of their lives after surgical treatment, but colorectal cancer can spread (metastasize) in up to 50% of patients. One of the most common areas colorectal cancer spreads to is the lungs, affecting up to 18% of patients with colorectal cancer. Detecting cancerous nodules in the lung early provides patients with the best outcomes, but there are no evidence-based standards for when and how often to screen colorectal cancer patients with chest CT or PET scans. Now, a new study has found that colorectal cancer patients with certain clinical characteristics may benefit from more frequent chest imaging to help identify and target cancer that has spread to the lungs. These findings have the potential to improve long-term outcomes of patients with metastatic colorectal cancer.

The study by researchers at the MD Anderson Cancer Center (Houston, TX, USA) investigated optimal timing intervals and key clinical factors, including genetic factors and tumor characteristics, that may reveal which patients are at risk for developing lung metastases. To identify which colorectal cancer patients may benefit from early chest imaging and at what time intervals, an interdisciplinary team of researchers – including cardiothoracic surgeons, colorectal cancer surgeons, and gastrointestinal oncologists – collaborated to investigate evidence-based surveillance guidelines for colorectal patients who are at risk of developing lung metastases.

Using two MD Anderson cancer databases that included both colorectal cancer patients and thoracic cancer patients, the study team retrospectively reviewed data from patients with colorectal cancer who did and did not develop lung metastases. Patients were grouped according to the development of lung metastases and the timing of their diagnosis. The team used statistical methods to investigate which clinical characteristics, such as age or genetic factors, correlated most with the risk of developing lung metastases. The findings of the study revealed that out of 1,600 patients with colorectal cancer, 233 (14.6%) developed pulmonary (lung) metastases, with a median time of 15.4 months following colorectal surgery. The team identified age, neoadjuvant or adjuvant systemic therapy (such as chemotherapy or immunotherapy), lymph node ratio, lymphovascular and perineural invasion (high-risk tumor characteristics observed under a microscope), and presence of KRAS genetic mutations as risk factors for developing lung metastases.

Further data analysis revealed that patients who required systemic therapy around the time of their surgical operation for colorectal cancer, who had an elevated lymph node ratio, and a KRAS mutation, were at risk of developing lung metastases within three months of surgery. The authors concluded that these patients may benefit from more frequent surveillance with chest CT or PET scans. The researchers noted that while these risk factors are not necessarily surprising from a clinical perspective, they highlight the need to adequately screen certain colorectal cancer patients after surgical treatment. In some cases, removing cancerous lung nodules surgically early on can significantly improve outcomes. In future research, the team plans to validate findings in a separate group of patients, with the hope of formalizing chest surveillance protocols for widespread clinical adoption. The researchers have noted that as colorectal cancer research evolves, sensitive blood tests to detect cancer or advanced radiographic screening methods using artificial intelligence may also play an important role in monitoring patients.

“After patients are diagnosed with colorectal cancer, many of them want to better understand what their cancer diagnosis entails in terms of their surveillance and survivorship for the rest of their life, but we currently lack data and uniform guidelines to support how often these patients should be screened with chest imaging,” said co-author Mara Antonoff, MD, FACS, associate professor, thoracic and cardiovascular surgery, UT MD Anderson Cancer Center. “With this study, we sought to develop a strategy that is evidence-based to determine how frequently, at what intervals, and for how long patients at risk of developing lung metastases should undergo imaging of their chest.”

“A concrete clinical application of this research, following validation, is to build evidence-based guidelines affecting chest surveillance in patients with resected colorectal cancer,” said Nathaniel Deboever, MD, general surgery resident, UTHealth Houston McGovern Medical School, and the lead author of the study. “These guidelines will hopefully allow high-risk patients to undergo radiographic screening in a timely manner, permitting the early diagnosis of pulmonary disease.” 

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