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Incoming links: Tumour grade
An historically appropriate classification distinguishes the hard, soft, gelatinous, pigmented and epithelial malignant growths, together with recurrent and destructive growths whose place in “cancer” was disputed. Modern classification instead distinguishes tumours by cellular lineage and biological behaviour.
The quotation marks around “Malignant” matter. In 1867 the clinical grouping did not have a single settled boundary in histology. Infiltration, destructive growth, return after removal, spread to distant sites and progressive constitutional illness were warning features; hardness or rapid growth alone was not a sufficient definition. A contemporary review of an 1866 textbook explicitly disputed confused descriptions of hard and soft cancer, illustrating that this was already a live diagnostic controversy.[ref]
Review of Demonstrations of Microscopic Anatomy (1866 book). Discussion under “tumours”, contrasting scirrhus with encephaloid, melanotic and colloid growths and rejecting an indiscriminate use of “cancer”
A useful period classification, without pretending that every contemporary author drew the same boundaries, is:
- Scirrhous carcinoma, or hard cancer. Abundant firm fibrous supporting tissue makes a hard, often contracted growth, classically in the breast. Retraction and fixation reflect invasion and contraction of that supporting tissue. “Hard” describes the gross appearance; it is not a separate modern cellular lineage.
- Encephaloid cancer, or medullary/soft cancer. The name refers to soft, brain-like tissue, often richly cellular and prone to rapid growth, breakdown and haemorrhage. The historical label could include more than one modern diagnosis; it does not mean a tumour of the brain.
- Colloid cancer. A gelatinous appearance associated with abundant mucin. Some such lesions would now be classified as mucinous carcinomas; appearance alone cannot retrospectively determine their modern identity.
- Melanotic tumour. Dark pigment supplied a gross category. Many malignant examples belong to modern melanoma, arising from melanocytes, but pigmentation is neither necessary nor sufficient for melanoma. Pigmented examples could also be treated as varieties within other period categories.
- Epithelioma, or epithelial cancer. A growth exhibiting epithelial structure, especially at skin and mucous membrane surfaces. Many examples correspond to squamous cell carcinoma. A locally destructive rodent ulcer, now generally basal cell carcinoma, was sometimes separated because distant spread was unusual.
- Recurrent fibroid tumour and related “fibroplastic” or other sarcomas. These could return repeatedly and invade locally despite differing from the period's typical cancer. They were sometimes called semi-malignant. A reported 1866 recurrent fibroid tumour developed distant deposits after apparently successful local treatment: a vivid reason that a purely local category could fail.[ref]St George's Hospital Reports (1866). Case of recurrent fibroid tumour of the thigh, subsequent constitutional disease and post-mortem deposits; terminology is the report's historical terminology
Those are overlapping historical descriptive groups, not six mutually exclusive modern diagnoses. Nor does every growth historically called “sarcoma” meet the modern definition of sarcoma.
The modern organising principle asks what cells are malignant. Carcinoma arises from epithelium; sarcoma arises in bone or soft tissue; melanoma arises from melanocytes; lymphoma and leukaemia concern blood-forming or immune cells. Other families include central nervous system and germ cell tumours. A solid lump is not essential for cancer. Within a family, histology, immunohistochemistry and appropriate molecular diagnostics refine the diagnosis. Tumour grade describes features of aggressiveness, whereas tumour stage describes extent of disease.[ref]
This also corrects the old inference that recurrence must reflect a mysterious constitutional deposit: local residual disease and metastasis are distinct mechanisms, and an apparently circumscribed growth may already have disseminated.