Page 212 - Textbook of Pathology, 6th Edition

196 good host immune attack, only to reappear as secondaries cardinal clinical features of malignant tumours are:
elsewhere in the body e.g. choriocarcinoma, malignant invasiveness and metastasis (discussed later).
melanoma. Gross appearance of benign and malignant tumours may
The regulation of tumour growth is under the control of be quite variable and the features may not be diagnostic on
growth factors secreted by the tumour cells. Out of various the basis of gross appearance alone. However, certain
growth factors, important ones modulating tumour biology distinctive features characterise almost all tumours compared
are listed below and discussed later: to neighbouring normal tissue of origin—they have a
i) Epidermal growth factor (EGF) different colour, texture and consistency. Gross terms such
ii) Fibroblast growth factor (FGF) as papillary, fungating, infiltrating, haemorrhagic, ulcerative
SECTION I
iii) Platelet-derived growth factor (PDGF) and cystic are used to describe the macroscopic appearance
iv) Colony stimulating factor (CSF) of the tumours. General gross features of benign and
v) Transforming growth factors-β (TGF-β) malignant tumours are as under (Figs. 8.2 and 8.3):
vi) Interleukins (IL) Benign tumours are generally spherical or ovoid in shape.
vii) Vascular endothelial growth factor (VEGF)
They are encapsulated or well-circumscribed, freely movable,
more often firm and uniform, unless secondary changes like
II. CANCER PHENOTYPE AND STEM CELLS haemorrhage or infarction supervene (Fig. 8.2,A, E).
Normally growing cells in an organ are related to the Malignant tumours, on the other hand, are usually
neighbouring cells—they grow under normal growth irregular in shape, poorly-circumscribed and extend into the
controls, perform their assigned function and there is a adjacent tissues. Secondary changes like haemorrhage,
balance between the rate of cell proliferation and the rate of infarction and ulceration are seen more often. Sarcomas
cell death including cell suicide (i.e. apoptosis). Thus normal typically have fish-flesh like consistency while carcinomas
cells are socially desirable. However, cancer cells exhibit anti- are generally firm (Fig. 8.2,C, G).
social behaviour as under:
i) Cancer cells disobey the growth controlling signals in the IV. MICROSCOPIC FEATURES
body and thus proliferate rapidly. For recognising and classifying the tumours, the microscopic
ii) Cancer cells escape death signals and achieve immortality. characteristics of tumour cells are of greatest importance.
iii) Imbalance between cell proliferation and cell death in These features which are appreciated in histologic sections
cancer causes excessive growth. are as under:
iv) Cancer cells lose properties of differentiation and thus 1. microscopic pattern;
General Pathology and Basic Techniques
perform little or no function. 2. cytomorphology of neoplastic cells (differentiation and
v) Due to loss of growth controls, cancer cells are genetically anaplasia);
unstable and develop newer mutations. 3. tumour angiogenesis and stroma; and
vi) Cancer cells overrun their neighbouring tissue and invade 4. inflammatory reaction.
locally.
vii) Cancer cells have the ability to travel from the site of 1. Microscopic Pattern
origin to other sites in the body where they colonise and
establish distant metastasis. The tumour cells may be arranged in a variety of patterns in
Cancer cells originate by clonal prolferation of a single different tumours as under:
progeny of a cell (monoclonality). Cancer cells arise from The epithelial tumours generally consist of acini, sheets,
stem cells normally present in the tissues in small number columns or cords of epithelial tumour cells that may be
and are not readily identifiable. These stem cells have the arranged in solid or papillary pattern (Fig. 8.2,B, D).
properties of prolonged self-renewal, asymmetric replication The mesenchymal tumours have mesenchymal tumour cells
and transdifferentiation (i.e. plasticity). These cancer stem arranged as interlacing bundles, fasicles or whorls, lying
cells are called tumour-initiating cells. Their definite existence separated from each other usually by the intercellular matrix
in acute leukaemias has been known for sometime and have substance such as hyaline material in leiomyoma (Fig. 8.2,E),
now been found to be present in some other malignant cartilaginous matrix in chondroma, osteoid in osteosarcoma,
tumours. reticulin network in soft tissue sarcomas etc (Fig. 8.2,H).

Certain tumours have mixed patterns e.g. teratoma arising
III. CLINICAL AND GROSS FEATURES from totipotent cells, pleomorphic adenoma of salivary gland
(mixed salivary tumour), fibroadenoma of the breast,
Clinically, benign tumours are generally slow growing, and carcinosarcoma of the uterus and various other combinations
depending upon the location, may remain asymptomatic (e.g. of tumour types.
subcutaneous lipoma), or may produce serious symptoms
(e.g. meningioma in the nervous system). On the other hand, Haematopoietic tumours such as leukaemias and
malignant tumours grow rapidly, may ulcerate on the lymphomas often have none or little stromal support.
surface, invade locally into deeper tissues, may spread to Generally, most benign tumours and low grade malignant
distant sites (metastasis), and also produce systemic features tumours reduplicate the normal structure of origin more
such as weight loss, anorexia and anemia. In fact, two of the closely so that there is little difficulty in identifying and