Spread of cancer to distant sites is by following routes:-
Lymphatic spread :-
•Generally, carcinomas spread by lymphatic route and sarcomas spread through hematogenous route.However few sarcomas may also spread by lymphatic route.
• Involvement of lymph nodes by malignant cells is by:-
– lymphatic permeation :- The walls of the lymphatics are readily invaded by cancer cells and may form continuous growth in lymphatic channels called lymphatic permeation.
– lymphatic emboli :- Malignant cells may detach to form tumour emboli that may be carried along to the next lymph node. Tumour emboli will enter the lymph node by convex surface and gets lodged in subcapsular sinus and start growing . Later the lymph node will be enlarged and will be replaced by malignant tumour.
Characteristics of lymphatic spread:-
• Regional lymph nodes are invariably involved producing regional nodal metastasis. From carcinoma of the breast to axillary lymph nodes ; from the carcinoma of thyroid to cervical lymph nodes and however all regional nodal enlargements are not because of nodal metastasis.
• And sometimes, Lymphatic metastasis do not develop in the 1st lymph node which is nearest to the tumour because of venous lymphatic anastomoses or due to radiation , obliteration of lymphatics by inflammation so called skip metastasis.
• Other times due to obstruction of lymphatics by the tumour cells the lymph flow is disturbed and the tumour cells spread against the flow of lymph causing retrograde metastasis at unusual sites. Metastasis of carcinoma prostate to supraclavicular lymph nodes.
• Virchows lymph node is nodal metastasis preferentially to supraclavicular lymph node from cancers of abdominal organs like cancer of stomach , colon.
Hematogenous spread :-
• Sarcomas usually spread by hematogenous route. And few carcinomas spread through hematogenous route.
Few features of hematogenous route are :-
• systemic veins drain blood to inferior vena cava from limbs , head and neck and pelvis so tumour of these organs will mostly metastasize to lungs.
• portal veins drains blood from bowel, pancreas and spleen to liver so, tumour of these organs are secondarily metastasize to liver.
Gross appearance of affected organ:-
There are multiple ; rounded nodules of varying size and scattered throughout the organ.
Microscopically:- primary tumour upon metastasis at different sites show varying degree of differentiation due to influence of local environment surrounding the tumour for its growth.
Spread along the body cavities and natural passages:-
• It’s the uncommon route of spread of tumour.
• Transcoelomic spread :- certain cancers invade through the serosal wall of the coelomic cavity so that the tumour cells or its fragments breaks off and will be carried in the coelomic fluid and gets implanted else where in the body. Most often involved is peritoneal cavity and less occasionally pleural and pericardial cavity.
– examples :- carcinoma of the stomach seeding to both ovaries (krukenberg tumour)
• Spread along the epithelium lined surfaces :- it’s unusual because intact epithelium and mucus are resistant to be penetrated by tumour cells. Examples :-are through the bronchus into alveoli.
• Spread via CSF:- Malignant tumours of ependyma and leptomeninges may spread by release of tumour cells through CSF.
• Implantation :- rare cases of reports of spread of some tumours is by implantation.
Reference :- Harsh mohan