Neoplasia

1. Definitions

   1. Neoplasia – the process of “new growth”

   2. Neoplasm – a new growth

      1. An abnormal mass of tissue, the growth of which exceeds and is uncoordinated with that of the normal tissues and persists in the same excessive manner after cessation of the stimuli which evoked the change.

      2. Three Key Features of Neoplasia

         1. Excessive tissue growth

         2. Lack of responsiveness to control mechanisms

         3. Lack of dependence on the continued presence of the stimulus

   3. Tumor – the term was originally applied to the swelling caused by inflammation, but by long precedent, the term is now equated with neoplasm

      1. Two Basic Components of All Tumors

         1. Proliferating neoplastic cells that constitute their parenchyma

         2. Supportive stroma made up of connective tissue and blood vessels

            1. Although parenchymal cells represent the proliferating “cutting edge” of neoplasms and so determine their behavior and pathologic consequences, the growth and evolution of neoplasms are critically dependent on their stroma.

            2. Stroma consists of fibrous connective tissue and vasculature

               1. The neoplasm with scant stromal support tends to be soft and fleshy

               2. Sometimes the parenchymal cells stimulate the formation of an abundant collagenous stroma, referred to as desmoplasia

               3. Some tumors such as some gastrointestinal carcinomas are stony hard or scirrhous

         3. There is cross-talk between tumor cells and stromal cells that appears to directly influence the growth of tumors.

      2. Tumors arise because of a partial or complete arrest in differentiation.

         1. top panel, During normal tissue renewal, normal stem cells undergo division and differentiation to produce a mature tissue type.

         2. lower 2 panels, During neoplastic growth, a maturation arrest leads to an accumulation of the tumor cells at the stage of differentiation of the transformed target tumor cell, vertical arrows. The stage of differentiation of the target cell and the subsequent maturation arrest determine the biological behavior (benign or malignant) of the tumor. Some portion of tumor cells escape the arrest and go on to differentiate and become mature, postmitotic cells. Thus, tumors are composed of neoplastic stem cells and their well differentiated progeny, which form caricature of their tissue of origin.

   4. Cancer – the common term for all malignant tumors

   5. Oncology – the study of tumors or neoplasm (Gr. oncos=tumor)

Category: Pathology Notes