Rectal cancer is a common malignant tumor of the gastrointestinal tract in China, and its incidence has shown an obvious increase in recent years. The treatment of rectal cancer is actually a complex system project, and the ultimate goal of treatment is not only to cure the tumor, but also to ensure the long-term quality of life of patients. For example, patients with low rectal cancer often need to have their anus removed and will have to wear an ostomy bag (fecal pocket) for the rest of their lives after surgery, which is a problem that seriously affects patients’ lives. Therefore, the treatment of rectal cancer is never as simple as an operation right away! Let me talk about how to diagnose rectal cancer. First of all, the diagnosis of rectal cancer needs pathological diagnosis, that is, only after colonoscopy and biopsy report is clear can rectal cancer be diagnosed. Secondly, it is necessary to clarify the tumor stage, which is what people call whether there is metastasis or not. The most common distant metastasis sites of rectal cancer are liver, lung and distant lymph nodes, and the method to determine whether there is metastasis is mainly imaging examination, such as CT, ultrasound, chest X-ray or nuclear magnetic examination. Lastly, the local staging of rectal cancer, that is, which layer of the intestinal wall has been invaded by the tumor? Is there any lymph node metastasis around the intestine? This will require transrectal endoluminal ultrasound or MRI. Nowadays, we have some more advanced examination methods to determine whether there is metastasis, which is PET-CT examination. This test can identify whether the tumor has spread throughout the body and is much more accurate than the usual imaging tests. However, PET-CT examination does not replace pathological diagnosis and local staging examination (transrectal endoluminal ultrasound or MRI), which is a misconception of many patients about this examination. Another misconception is that rectal cancer requires immediate surgery once it is diagnosed. Indeed, rectal cancer examinations often take a period of time to be perfected because many of them require appointment in line, so some patients mistakenly believe that the sooner surgery is performed after diagnosis, the better, otherwise the tumor will metastasize. This is a complete misunderstanding. In fact, it takes years for rectal cancer to occur, and the week you need for the examination will not be anything at all. And if you blindly operate because of imperfect examination, it is likely to result in irregular treatment, and the ultimate loss is yourself.