Describe the specific cellular and molecular events that characterize the transition from carcinoma in situ to invasive squamous cell carcinoma.

Carcinoma in situ (CIS) represents a pre-invasive stage of cancer where malignant epithelial cells are confined to the epithelium and have not yet penetrated the basement membrane, a specialized layer of extracellular matrix that separates epithelial cells from the underlying connective tissue, known as the stroma. The transition to invasive squamous cell carcinoma is characterized by the breakdown of this physical barrier and the subsequent infiltration of malignant cells into the stroma.