Adjuvant therapy is therapy (usually chemotherapy, but could also be endocrine therapy, radiotherapy etc) that is given following surgical removal of the cancer. No known cancer has been left according to the pathological examination of the tumour or according to clinial examination or the imaging investigations performed. However, many of these patients succumb to their cancer subsequently, due to this undetectable disease. It has been discovered that the outlook for many of these patients can be improved by an extra course (adjuvant) of therapy.
We now know that many patients with colorectal cancer (and other cancers) have tumour cells present in their bone marrow. These are termed micro-metastases that can only be identified by special staining of samples of bone marrow. The prevelance of patients with micro-metastases appears to be greater than the number of patients that succumb to the cancer, therefore, not all micrometastases will cause systemic cancer.
Neo-adjuvant therapy, is therapy (usually chemo and radiotherapy together) that is given prior to surgical removal of the tumour. This method of treating cancers has been shown to be beneficial in locally advanced rectal cancer (T3 and T4) and there is some controversy about its benefit in esophageal and gastric cancers.