Page 140 - Concise Pathology for Exam Preparation ( PDFDrive )

6 Neoplasia 125

Mature adipose
tissue

Capsule

FIGURE 6.1. Lipoma composed of mature adipocytes and surrounded by a well-formed
capsule indicating its benign nature (H&E; 1003).

Presently, tissue of origin and behavioural pattern is the basis of classification of most
neoplasms.

Q. Define and classify benign tumours?
Ans. Benign tumours are neoplasms, which grow as cohesive expansile masses, which do
not invade, infiltrate or metastasize. They are usually encapsulated. (The capsule is made
of a rim of compressed connective tissue derived largely from the native stroma.)
Nomenclature and Classification
1. Tumours of mesenchymal origin: Designated by adding suffix ‘oma’ to the cell of
origin, eg, fibroma, lipoma (Fig. 6.1), osteoma and chondroma.
2. Tumours of epithelial origin are variously classified:
(a) Some based on the cell of origin, eg, squamous cell carcinoma.
(b) Others based on the microscopic architecture, eg, adenoma (glandular pattern),
papilloma (finger-like or warty projections), cystadenoma, (cystic masses) and
papillary cyst adenoma (papillary cystic masses)
3. Mixed tumours: Divergent differentiation of a single line of parenchymal cells resulting
in tumours comprised more than one cell type; usually derived from one germ cell
layer, eg, pleomorphic adenoma of the salivary gland.

Q. Define differentiation?
Ans. Differentiation is the extent to which neoplastic cells resemble comparable normal
cells, both morphologically and functionally.
• The cells in benign tumours are almost always well differentiated and resemble their
normal cells of origin. Cancers, however, vary from being well differentiated to poorly
differentiated.
• Well-differentiated cancers show progressive maturation or specialization of
undifferentiated cells as they proliferate. Poorly differentiated or undifferentiated
cancers show proliferation without differentiation or maturation.
• Well-differentiated squamous cell carcinomas of the epidermis elaborate keratin, just
as well-differentiated hepatocellular carcinomas elaborate bile. Highly anaplastic
undifferentiated cells, whatever is their tissue of origin, loose their resemblance to the
normal cells from which they have arisen.

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