Carcinoma in situ is synonymous with high grade dysplasia in most organs. The risk of transforming into cancer is high. Treatment is still usually easy.
Invasive carcinoma, commonly called cancer, is the final step in this sequence. It is a disease which, when left untreated, will invade the host (hence its name) and will probably kill them. It can often, but not always, be treated successfully.
Metaplasia is a situation where cells have changed from their original mature differentiated type into another mature differentiated cell type as an adaptive response to exposure to chronic irritation, or to a pathogen or carcinogen. It also occurs where one normal cell type changes into another normal cell type as in the cervix where squamous epithelium on the exo-cervix changes to normal columnar epithelium in the endo-cervix.
This area is also known as the transformation zone and is the location of many dyplastic lesions thus the sampling of this area during a pap test is critical. Metaplasia is distinct from dysplasia because in a dysplastic cell these changes have become encoded into the genome and so are heritable or passed on to daughter cells during cell replication.
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