Which of the following is often biopsied to assess the presence of metastatic lesion in lymph nodes?

A  “sentinel lymph node”  is the first regional lymph node that receives lymph flow from a primary tumor. It can be identified by injection of blue dyes or radiolabeled tracers near the primary tumor. Biopsy of sentinel lymph nodes allows determination of the extent of spread of tumor and can be used to plan treatment. Reference-Robbins BASIC PATHOLOGY 10th edition pg-196