A lesion 3cms away from gastroesophageal junction contain columnar epithelium ,such a type of lesion is
Correct Answer: Metaplasia
Description: Ref Robbins 8/e p10,265,;9/e p271 Metastasis Metastases are secondary implants of a tumor that are dis- continuous with the primary tumor and located in remote tissues (Fig. 5-11). More than any other attribute, the propey of metastasis identifies a neoplasm as malignant. Not all cancers have equivalent ability to metastasize, however. At one extreme are basal cell carcinomas of the skin and most primary tumors of the central nervous system, which are highly invasive locally but rarely metastasize. At the other extreme are osteogenic (bone) sarcomas, which usually have metastasized to the lungs at the time of initial discovery. Approximately 30% of patients with newly diagnosed solid tumors (excluding skin cancers other than melano- mas) present with clinically evident metastases. An additional 20% have occult (hidden) metastases at the time of diagnosis. In general, the more anaplastic and the larger the primary neoplasm, the more likely is metastatic spread, but as with most rules, there are exceptions. Extremely small cancers have been known to metastasize; conversely, some large and ominous-looking lesions may not. Dissemination strongly prejudices, and may preclude, the possibility of curing the disease, so obviously, sho of prevention of cancer, no achievement would confer greater benefit on patients than the prevention of metastases. Malignant neoplasms disseminate by one of three path- ways: (1) seeding within body cavities, (2) lymphatic spread, or (3) hematogenous spread. Spread by seeding occurs when neoplasms invade a natural body cavity. This mode of dissemination is paicularly characteristic of cancers of the ovary, which often cover the peritoneal sur- faces widely. The implants literally may glaze all peritoneal surfaces and yet not invade the underlying tissues. Here is an instance of the ability to reimplant elsewhere that seems to be separable from the capacity to invade. Neoplasms of the central nervous system, such as a medulloblastoma or ependymoma, may penetrate the cerebral ventricles and be carried by the cerebrospinal fluid to reimplant on the men- ingeal surfaces, either within the brain or in the spinal cord. Lymphatic spread is more typical of carcinomas, whereas hematogenous spread is ored by sarcomas. There are numerous interconnections, however, between the lym- phatic and vascular systems, so all forms of cancer may disseminate through either or both systems. The pattern of lymph node involvement depends principally on the site of the primary neoplasm and the natural pathways of local lymphatic drainage. Lung carcinomas arising in the respi- ratory passages metastasize first to the regional bronchial lymph nodes and then to the tracheobronchial and hilar nodes. Carcinoma of the breast usually arises in the upper outer quadrant and first spreads to the axillary nodes. However, medial breast lesions may drain through the chest wall to the nodes along the internal mammary aery. Thereafter, in both instances, the supraclavicular and infra- clavicular nodes may be seeded. In some cases, the cancer cells seem to traverse the lymphatic channels within the immediately proximate nodes to be trapped in subsequent lymph nodes, producing so-called skip metastases. The cells may traverse all of the lymph nodes ultimately to reach the vascular compament by way of the thoracic duct. A "sentinel lymph node" is the first regional lymph node that receives lymph flow from a primary tumor. It can be identified by injection of blue dyes or radiolabeled tracers near the primary tumor. Biopsy of sentinel lymph nodes allows determination of the extent of spread of tumor and can be used to plan treatment. Of note, although enlargement of nodes near a primary neoplasm should arouse concern for metastatic spread, it does not always imply cancerous involvement. The necrotic products of the neoplasm and tumor antigens often evoke immunologic responses in the nodes, such as hyperplasia of the follicles (lymphadenitis) and proliferation of macro- phages in the subcapsular sinuses (sinus histiocytosis). Thus, histopathologic verification of tumor within an enlarged lymph node is required. Hematogenous spread is the ored pathway for sarco- mas, but carcinomas use it as well. As might be expected, aeries are penetrated less readily than are veins. With venous invasion, the blood-borne cells follow the venous flow draining the site of the neoplasm, with tumor cells often stopping in the first capillary bed they encounter. Since all poal area drainage flows to the liver, and all caval blood flows to the lungs, the liver and lungs are the most frequently involved secondary sites in hematogenous dissemina- tion. Cancers arising near the veebral column often em- bolize through the paraveebral plexus; this pathway probably is involved in the frequent veebral metastases of carcinomas of the thyroid and prostate. Ceain carcinomas have a propensity to grow within veins. Renal cell carcinoma often invades the renal vein to grow in a snakelike fashion up the inferior vena cava, sometimes reaching the right side of the hea. Hepatocel- lular carcinomas often penetrate poal and hepatic radicles to grow within them into the main venous channels. Remarkably, such intravenous growth may not be accom- panied by widespread dissemination. Many observations suggest that the anatomic localiza- tion of a neoplasm and its venous drainage cannot wholly explain the systemic distributions of metastases. For example, prostatic carcinoma preferentially spreads to bone, bronchogenic carcinomas tend to involve the adre- nals and the brain, and neuroblastomas spread to the liver and bones. Conversely, skeletal muscles, although rich in capillaries, are rarely the site of secondary deposits. The molecular basis of such tissue-specific homing of tumor cells is discussed later on.
Category:
Anatomy
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