Approximately 20-30 % of colon cancer patients who have no metastasis in lymph nodes after definitive colectomy have recurrence with distant metastasis. These recurrences could be due to missed occult tumor cells or micrometastasis. Detailed examination of all lymph nodes is expensive and time consuming. Sentinel lymph node mapping using Indocyanine green dye helps in identifying the lymph nodes which are most likely to harbour metastasis. These sentinel lymph nodes can be subsequently subjected to detailed pathologic examination and immunohistochemistry which increases the likelihood of identifying micrometastasis and occult tumor cells. Patients found to harbour such metastasis can be treated with additional chemotherapy after surgery. The aim of the study is to examine the feasibility of sentinel lymph node mapping using Indocyanine green dye in colon cancer and evaluate the upstaging rate in post-operative colon cancer patients who don't have metastatic lymph nodes on routine histopathology.

All patients of colon cancer fulfilling the inclusion criteria and excluding the patients according to the exclusion criteria will undergo standard laparoscopic/open colectomy.

Indocyanine green dye is injected around the tumor in subserosal location for open surgeries and submucosally after on-table colonoscopy for laparoscopic surgeries and followed with near-infrared scope. Patients will undergo intra-operative on-table colonoscopy after induction of anesthesia. All sentinel nodes will be marked with clips/sutures for identification by the pathologist post-operatively. Any aberrant lymph nodes identified outside the planned resection margins will be excised, marked with the position of excision and sent separately from the gross specimen. After this the surgeon will proceed with the surgery including vascular ligation and resection of mesocolon.

After surgery, all the lymph nodes identified in the specimen including the tagged sentinel lymph nodes will be examined using standard Hematoxylin and eosin staining. If all the lymph nodes are negative for metastasis, the sentinel lymph nodes will undergo additional stepwise sections and immunohistochemistry for pancytokeratin.

Inclusion criteria:

Age 18 years or older Biopsy proven colon cancer Scheduled for laparoscopic/open colectomy

Exclusion criteria:

Prior colorectal surgery Gross lymph node invasion on pre-operative imaging or intraoperative staging Advanced disease (T4 disease or metastasis) on preoperative imaging or intraoperative staging Allergy to iodide containing compounds, human albumin or Indocyanine green dye History of hyperthyroidism or thyroid adenoma Palliative surgery Advanced hepatic failure Advanced renal failure

The pathologist involved in routine histological assessment of the resected lymph nodes including lymph nodes in the gross specimen and sentinel lymph nodes will be blinded to the identity of the sentinel lymph nodes.