Page 216 - Textbook of Pathology, 6th Edition

200 discontinuous secondary tumour mass/masses are formed
at the site of lodgement. Metastasis and invasiveness are the
two most important features to distinguish malignant from benign
tumours: benign tumours do not metastasise while all the
malignant tumours with a few exceptions like gliomas of the
central nervous system and basal cell carcinoma of the skin,
can metastasise. Generally, larger, more aggressive and
rapidly-growing tumours are more likely to metastasise but
there are numerous exceptions. About one-third of malignant
SECTION I
tumours at presentation have evident metastatic deposits
while another 20% have occult metastasis.

Routes of Metastasis
Cancers may spread to distant sites by following pathways:
1. Lymphatic spread
2. Haematogenous spread
3. Spread along body cavities and natural passages
(Transcoelomic spread, along epithelium-lined surfaces,
Figure 8.10 Inflammatory reaction in the stroma of the tumour. A, spread via cerebrospinal fluid, implantation).
Lymphocytic reaction in seminoma testis. B, Granulomatous reaction
(thick arrow) in Hodgkin’s lymphoma (thin arrow for RS cell). 1. LYMPHATIC SPREAD. In general, carcinomas metastasise
by lymphatic route while sarcomas favour haematogenous route.
macrophages, and in some instances granulomatous reaction, However, sarcomas may also spread by lymphatic pathway.
in the absence of ulceration. This is due to cell-mediated The involvement of lymph nodes by malignant cells may be
immunologic response by the host in an attempt to destroy of two forms:
the tumour. In some cases, such an immune response
improves the prognosis. i) Lymphatic permeation. The walls of lymphatics are readily
The examples of such reaction are: seminoma testis invaded by cancer cells and may form a continuous growth
(Fig. 8.10), malignant melanoma of the skin, lympho- in the lymphatic channels called lymphatic permeation.
epithelioma of the throat, medullary carcinoma of the breast, ii) Lymphatic emboli. Alternatively, the malignant cells may
choriocarcinoma, Warthin’s tumour of salivary glands etc. detach to form tumour emboli so as to be carried along the
General Pathology and Basic Techniques
lymph to the next draining lymph node. The tumour emboli
V. LOCAL INVASION (DIRECT SPREAD) enter the lymph node at its convex surface and are lodged in
BENIGN TUMOURS. Most benign tumours form the subcapsular sinus where they start growing (Fig. 8.11).
encapsulated or circumscribed masses that expand and push Later, of course, the whole lymph node may be replaced and
aside the surrounding normal tissues without actually enlarged by the metastatic tumour (Fig. 8.12).
invading, infiltrating or metastasising. Generally, regional lymph nodes draining the tumour are
invariably involved producing regional nodal metastasis e.g.
MALIGNANT TUMOURS. Malignant tumours also enlarge from carcinoma breast to axillary lymph nodes, from
by expansion and some well-differentiated tumours may be carcinoma thyroid to lateral cervical lymph nodes,
partially encapsulated as well e.g. follicular carcinoma bronchogenic carcinoma to hilar and para-tracheal lymph
thyroid. But characteristically, they are distinguished from nodes etc.
benign tumours by invasion, infiltration and destruction of the However, all regional nodal enlargements are not due to
surrounding tissue, besides distant metastasis (described nodal metastasis because necrotic products of tumour and
below). In general, tumours invade via the route of least
resistance, though eventually most cancers recognise no antigens may also incite regional lymphadenitis of sinus
anatomic boundaries. Often, cancers extend through tissue histiocytosis.
spaces, permeate lymphatics, blood vessels, perineural Sometimes lymphatic metastases do not develop first in
spaces and may penetrate a bone by growing through the lymph node nearest to the tumour because of venous-
nutrient foramina. More commonly, the tumours invade thin- lymphatic anastomoses or due to obliteration of lymphatics
walled capillaries and veins than thick-walled arteries. Dense by inflammation or radiation, so called skip metastasis.
compact collagen, elastic tissue and cartilage are some of the Other times, due to obstruction of the lymphatics by
tissues which are sufficiently resistant to invasion by tumour cells, the lymph flow is disturbed and tumour cells
tumours. spread against the flow of lymph causing retrograde metastases
Mechanism of invasion of malignant tumours is discussed at unusual sites e.g. metastasis of carcinoma prostate to the
together with that of metastasis below. supraclavicular lymph nodes, metastatic deposits from
bronchogenic carcinoma to the axillary lymph nodes.
VI. METASTASIS (DISTANT SPREAD) Virchow’s lymph node is nodal metastasis preferentially
Metastasis (meta = transformation, stasis = residence) is to supraclavicular lymph node from cancers of abdominal
defined as spread of tumour by invasion in such a way that organs e.g. cancer stomach, colon, and gall bladder.