Which event signifies the start of the first course of treatment for rectal cancer?

The event that signifies the start of the first course of treatment for rectal cancer is the resection of rectal cancer. This is the procedure where the tumor is surgically removed along with some of the surrounding healthy tissue to ensure complete removal of the cancerous area. It represents a definitive intervention aimed at treating the disease and is typically considered the beginning of active treatment.

While a rectal biopsy is important for diagnosing cancer and an excisional biopsy of a lymph node may help determine the extent of disease spread, these are not considered treatment events. Similarly, radiation therapy may be part of a treatment plan, but it usually occurs after the initial surgical intervention has taken place and is not the starting point of treatment. Thus, resection directly addresses the rectal cancer itself, marking it as the essential first step in the treatment journey.