Interpreting the Complex Epithelium

Complex, or multilayered, epithelia (squamous and urothelial) may progress through a spectrum of changes, from benign hyperplasia and/or metaplasia, to inflamed reactive atypia, to dysplasia, to carcinoma in situ (CIS), to invasive carcinoma (crossing the basement membrane). The progression is not inevitable or consistent, and some lesions will regress. However, true dysplasia is generally regarded as a premalignant condition. Carcinoma in situ is one step from invasive cancer and therefore treated aggressively. Some lesions are easily monitored clinically, such as those in the cervix and oral cavity, and therefore each phase of change can be seen, biopsied, and followed. Others, such as in the nasopharynx, are generally not noticed until they are fairly large and/or symptomatic. This chapter will touch on basic principles that these epithelial layers have in common and introduce some organ systems that are covered in greater detail later in the book.