Invasive carcinoma differs from carcinoma in situ by: March 2005

Ans. C: Breached basement membrane Carcinoma in situ (CIS) is an early form of carcinoma. When dysplastic changes are marked and involves the entire thickness of the epithelium but the leasion remains confined by the basement membrane, it is referred to as carcinoma in situ. Once the tumour cells breach the basement membrane, the tumour is said to be invasive. For example, carcinoma in situ of the skin, also called Bowen's disease, is the accumulation of neoplastic epidermal cells within the epidermis only. For this reason, CIS will usually not form a tumour. Rather, the lesion is flat (in the skin, cervix, etc) or follows the existing architecture of the organ (in the breast, lung, etc). Some CIS, however, form tumours, for example colon polyps or papillary cancer of the bladder as well as some CIS of the breast (more properly called Ductal Carcinoma in situ). Many forms of invasive carcinoma originate from a CIS lesion. Therefore, CIS is considered a precursor or incipient form of cancer that may, if left untreated long enough, transform into a malignant neoplasm. These terms are related since they represent the three steps of the progression toward cancer: Dysplasia is the earliest form of pre-cancerous lesion recognizable in a biopsy Dysplasia can be low grade or high grade. The risk of low-grade dysplasia transforming into cancer is low. Carcinoma in situ is synonymous with high-grade dysplasia in most organs. The risk of transforming into cancer is high. Invasive carcinoma, commonly called cancer, is the final step in this sequence.