Get the Latest health and medical information delivered direct to your inbox! Squamous cell carcinoma: Cancer that begins in squamous cells -- thin, flat cells that look under the microscope like fish scales.Squamous cells are found in the tissue that forms the surface of the skin, the lining of hollow organs of the body, and the passages of the respiratory and digestive tracts.et the Latest health and medical information delivered direct to your inbox! Squamous cell carcinoma: Cancer that begins in squamous cells -- thin, flat cells that look under the microscope like fish scales.