Page 877 - Textbook of Pathology, 6th Edition

iv) Pallisaded arrangement: is characteristically seen in 4. Electron microscopy: EM as such is mainly a research 861
schwannomas in which the nuclei of tumour cells are piled tool and does not have much diagnostic value in soft tissue
upon each other. tumours but can be applied sometimes to look for
v) Biphasic pattern: is the term used for a combination tonofilaments or cell organelles.
arrangement of two types—fascicles and epithelial-like e.g. 5. Cytogenetics: Many soft tissue tumours have specific
in synovial sarcoma. genetic and chromosomal changes which can be done for
2. Cell types: After looking at the pattern of cells described determining histogenesis, or for diagnosis and prognosis.
above, preliminary categorisation of soft tissue tumours is GRADING. The number of pathological grades of soft tissue
done on the basis of cell types comprising the soft tissue tumours may vary according to different grading systems:
tumour:
2 grade system (grade I-II as low and high grade), 3-grade
i) Spindle cells: These are the most common cell types in system (grade I, II, III as low, intermediate and high grade)
most sarcomas. However, there are subtle differences in and 4 grade system (grade I-IV). Pathological grading is
different types of spindle cells e.g. based on following 3 features:
a) Fibrogenic tumours have spindle cells with light pink i) Tumour differentiation or degree of cytologic atypia
cytoplasm and tapering-ended nuclei. ii) Mitotic count
b) Neurogenic (Schwann cell) tumours have tumour cells similar iii) Tumour necrosis
to fibrogenic cells but have curved nuclei.
c) Leiomyomatous tumours have spindle cells with blunt-ended STAGING. Different staging systems for soft tissue sarcomas
(cigar-shaped) nuclei and more intense eosinophilic have been described but two of the most accepted staging
cytoplasm. systems are Enneking’s staging and American Joint Committee
d) Skeletal muscle tumours have spindle cells similar to (AJC) staging system:
leiomyomatous cells but in addition have cytoplasmic Enneking’s staging: This staging system is accepted by most
striations. oncologists and is based on grade and location of tumour as
ii) Small round cells: Some soft tissue sarcomas are under:
characterised by dominant presence of small round cells or According to tumour location: T1 (intracompartmental) and CHAPTER 29
blue cells and are termed by various names such as malignant T2 (extracompartmental) tumours.
small round cell tumours, round cell sarcomas, or blue cell According to tumour grade : G1 (low grade) and G2 (high
tumours (due to presence of lymphocyte-like round nuclear grade) tumours.
size and dense blue chromatin). Examples of this group of Accordingly, the stages of soft tissue tumours vary from
tumours are as under: stage I to stage III as under:
a) Rhabdomyosarcoma (embryonal and alveolar types) Stage I: G1 and T1-T2 tumours, but no metastases.
b) Primitive neuroectodermal tumour (PNET) Stage II: G2 and T1 -T2 tumours, but without metstases.
c) Ewing’s sarcoma Stage III: G1 or G2 , T1 or T2 tumours, but with metastases.
d) Neuroblastoma AJC staging: This AJC system of staging is similar to
e) Malignant lymphomas. staging for other tumours. It is based on TNM system in Soft Tissue Tumours
A few examples of epithelial tumours such as small cell which the primary tumor (T), the status of lymph nodes
carcinoma and malignant carcinoid tumours enter in the (N) and presence or absence of metastases (M) are taken
differential diagnosis of small round cell tumours. into consideration for staging, besides the histologic grade
of the tumour.
iii) Epithelioid cells: Some soft tissue tumours have either After these brief general comments, some important
epithelioid cells as the main cells (e.g. epithelioid sarcoma) examples of tumours of different types of mesenchymal
or have epithelial-like cells as a part of biphasic pattern of tissue origin are described below.
the tumour (e.g. synovial sarcoma).
3. Immunohistochemistry: Soft tissue tumours are TUMOURS AND TUMOUR-LIKE
distinguished by application of immunohistochemical stains.
Antibody stains are available against almost each cell LESIONS OF FIBROUS TISSUE
constituent. Based on differential diagnosis made on routine Fibromas, fibromatosis and fibrosarcoma are benign, tumour-
morphology, the panel of antibody stains is chosen for like, and malignant neoplasms respectively, of fibrous
applying on paraffin sections for staining. Some common connective tissue.
examples are as under:
i) Smooth muscle actin (SMA): for smooth muscle tumours. FIBROMAS
ii) Vimentin: as common marker to distinguish mesenchymal
cells from epithelium. True fibromas are uncommon tumours in soft tissues. Many
iii) Desmin: for skeletal muscle cells. fibromas are actually examples of hyperplastic fibrous tissue
iv) S-100: for nerve fibres. rather than true neoplasms. On the other hand, combinations
v) Factor VIII: antigen for vascular endothelium. of fibrous growth with other mesenchymal tissue elements
vi) LCA (leucocyte common antigen): common marker for are more frequent e.g. neurofibroma, fibromyoma etc.
lymphoid cells. Three types of fibromas are distinguished: