What part of the epithelial tissue must be degraded to allow tumor spread to other body parts?

The correct answer is the basal lamina. The basal lamina is a thin layer of extracellular matrix that provides support and anchorage for epithelial cells. It acts as a barrier that separates epithelial tissues from the underlying connective tissues. For tumor cells to invade surrounding tissues and metastasize to other parts of the body, they often need to breach this layer.

Degrading the basal lamina allows cancer cells to access the underlying stroma, which contains blood vessels, lymphatic vessels, and other supportive cells. This invasion is a critical step in the metastatic process, allowing tumor cells to migrate to different sites and form secondary tumors.

In contrast, tight junctions serve to maintain the integrity and barrier function of epithelial layers, preventing substances and cells from passing between them. Apical membrane proteins are involved in transporting substances and maintaining cell polarity, but they do not play a direct role in the invasion process. Integrin receptors are indeed important for cell adhesion and signaling, but they would not be the primary structure that needs to be degraded for tumor spread; their breakdown alone would not facilitate the same direct access as the degradation of the basal lamina.