What is a CTC examination?

For cancer patients, a blood test known as circulating tumor cell (CTC) analysis can detect whether the tumor has metastasized via the bloodstream. Some small, early-stage cancers or tiny metastatic lesions may be difficult to identify on CT imaging; in such cases, CTC testing represents the most accurate and clinically meaningful diagnostic tool. So, what exactly is CTC testing? Below, we provide a detailed explanation.

What is CTC testing?

CTC testing—short for “circulating tumor cell” testing—is a recently developed liquid biopsy technique. It primarily detects and quantifies circulating tumor cells (CTCs) present in peripheral blood to aid diagnosis. By analyzing the number of CTCs, as well as their protein expression profiles and genetic sequences, clinicians can obtain critical information regarding tumor biology and behavior. Malignant tumors commonly disseminate through the bloodstream to distant organs, and metastasis remains the leading cause of cancer-related death. Tumor cells first invade surrounding tissues adjacent to the primary tumor, then enter the blood or lymphatic circulation, forming CTCs. These CTCs travel to distant sites, extravasate from vessels, adapt to new microenvironments, and ultimately “seed,” proliferate, and colonize to form metastatic lesions. Therefore, early detection of CTCs in blood holds significant clinical value for predicting patient prognosis, evaluating treatment efficacy, and guiding personalized therapeutic strategies.

Knowledge Expansion: Who Should Undergo CTC Testing?

1. Individuals at High Risk for Cancer—Suitable for Early Screening

Early cancer detection relies on identifying CTCs in the blood of apparently healthy individuals. Annual CTC testing is recommended to detect malignancies at their earliest (even embryonic) stage, thereby maximizing the chance of cure. For high-risk populations—including those with a family history of cancer, HPV-positive individuals, patients with chronic hepatitis, chronic gastritis, or chronic colitis, long-term smokers, individuals frequently exposed to toxic or hazardous substances, those experiencing suboptimal health status with high stress or mental tension, and individuals identified by genetic testing as having elevated cancer susceptibility—we recommend CTC testing every three to six months.

2. Cancer Patients Currently Undergoing Treatment

A marked decrease or disappearance of CTCs indicates that the patient is likely benefiting from current therapy; thus, CTC testing is advised prior to each treatment cycle. Conversely, persistently rising or non-declining CTC counts suggest poor early treatment response or development of drug resistance, potentially signaling disease progression. In such cases, comprehensive clinical evaluation—including integration of CTC results with other diagnostic modalities—should be conducted by an oncology specialist to assess the risk of disease deterioration.

The above provides an overview of what CTC testing entails. We hope this information proves helpful to you.