Pathways of metastasisDistant metastasis of cancers may occur through one of three pathways.1.  Direct seeding of body cavities or surfaceIt occurs when a malignant neoplasm penetrates into a natural open field. Most common cavity involved is peritoneal cavity, but other cavities may also be involved, e.g., pleural, pericardial, joint space, subarachnoid. Such seeding is particularly characteristic of carcinomas arising in the ovaries. Sometimes mucus secreting tumor of appendix (or less commonly ovary) fill the peritoneal cavity with a gelatinous neoplastic mass referred to as pseudomyxoma peritonei.2.  Lymphatic spreadThis is the most common method of metastasis for carcinomas. Sarcoma may also use this route. As tumors do not have lymphatics, this type of spread takes place through the lymphatic vessels located at the tumor margins. The pattern of lymph node involvement follows the natural routes of lymphatic drainage. The first node in a regional lymphatics that receives lymph flow from the primary tumor is called sentinel lymphnode. Some times local lymph nodes may be bypassed because of venous lymphatic anastomosis skip metastasis.3.  Hematogenous spreadIt is typical of sarcomas but is also seen in carcinomas. Veins are more commonly involved than arteries because veins have thinner walls that can be penetrated readily, in contrast arteries have thicker walls. With venous invasion, the tumor cells in blood follow the venous flow draining the site of neoplasm. So, liver and lung are the most frequent organs involved in hematogenous spread because all portal area drainage flows to the liver and all caval blood flows to the lung. Arterial spread may occur when tumor cells pass through the pulmonary capillary beds or pulmonary A-V shunts or when pulmonary metastasis give rise to additional tumor emboli.