When is chemotherapy or radiotherapy indicated before surgery in colon cancer based on tumor stage?

Chemotherapy or radiotherapy prior to surgery in colon cancer is indicated primarily for tumors classified as T3-4 or N+ (node positive) due to the increased likelihood of residual disease and recurrence associated with these higher stage tumors.

In T3 tumors, the cancer has grown through the muscularis propria and into the subserosa, and T4 tumors have invaded adjacently into other tissues or organs. In both cases, the risk of metastasis or local recurrence is higher, thereby justifying preoperative therapy to shrink the tumor or to decrease the extent of surgery required, potentially improving surgical outcomes and overall survival.

Additionally, when lymph nodes are involved (N+), it signifies a higher risk of systemic disease spread, which makes neoadjuvant therapy valuable not only for local disease control before surgery but also to address potential micrometastatic disease. This approach allows for a better assessment of tumor response and may lead to more effective adjuvant therapy following surgical resection.

The other options describe scenarios where chemotherapy or radiotherapy is not routinely indicated. For instance, tumors classified as T1-2 or with no nodal involvement are generally manageable with surgical resection alone because they are less aggressive and have a favorable prognosis. Therefore