How is "Carcinoma in situ" defined?

"Carcinoma in situ" is defined as tumor cells that are localized and have not extended beyond the point of origin in the tissue. This means that the cancerous cells are present in the epithelial layer and have not invaded surrounding tissues. The significance of this definition lies in its implication for prognosis and treatment; since the carcinoma is confined to its original location, it is often considered highly treatable and has a better outcome compared to malignant tumors that have metastasized.

The other choices inaccurately describe carcinoma in situ. The presence of malignant tumors that have spread refers to invasive cancers, while benign tumors and non-malignant tumors do not fit the definition of carcinoma, which is specific to malignancy. Understanding this distinction is crucial for proper diagnosis and management of cancerous lesions.