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| Cancer classification |
Histo-pathology study | |
Histopathology classification is one of the most essential criteria for tumour classification. Here are a few examples:
Small cell lung carcinoma has a very distinct prognosis as compared to other histopathologic forms, like for instance epidermoid tumours. In the past, its prognosis was catastrophic (survival of only a few months). Its sensitivity to chemotherapy is very strong, thus offering a few cases of long remission. On the contrary, pulmonary adenocarcinomas are generally peripheral tumours with a slower development than epidermoid cancer, and that can often be treated by surgery.
Thus, lung cancer per se does not exist and studies should only compare similar histologies (with a simple differentiation between 'small cell lung carcinoma' and 'non-small cell lung carcinoma').
There are two very distinct histological forms of thyroid carcinoma: papillary carcinomas (more or less differentiated) are generally slow developing tumours which are, for a prolonged period of time, even when they give birth to metastases, sensitive to metabolic irradiation through radioactive Iodine doses, whereas medullary thyroid carcinoma is a rarer disease with a very characteristic elevation of calcitonin secretion, a relatively rapid evolution, and that is not particularly reactive to any kind of therapy.
Testis tumours have a similar spontaneous evolution whatever their histology. However seminoma are very sensitive to low doses of radiotherapy (and in fact to chemotherapy) whereas 'non-seminomatous' testis tumours (a very heterogeneous group) are not very sensitive to radiotherapy but generally very sensitive to chemotherapy. Some histological forms (in particular chorio-carinomatous forms) have an even quicker disease progression but seem to have differing sensitivity to chemotherapy. Tumour markers are very important for the classification of testis tumours.
Lymphomas need a very precise pathological analysis in order to distinguish Hodgkin’s lymphoma from other types (non-Hodgkin’s lymphoma) with various classifications attempting to improve differentiation among a variety of prognoses. Molecular biology and immunochemistry are now very important tools for their classification.
Within the same general histological classification (adenocarcinoma), various degrees of differentiation exist. For breast cancer, the Scarff, Bloom and Richardson classification enables us to distinguish poorly differentiated tumours which are prone to quickly metastasise, even in apparently localised tumours, and which should lead to the systematic prescription of adjuvant chemotherapy.
The same reasoning can be made for prostate cancer which has a great histological heterogeneity among specimens from the same patient: Gleason proposed a grading system (Gleason classification) which adds the most frequently observed differentiation of a patient's tumour to its less frequently observed differentiated aspect. For instance a Gleason grading (2 + 4) means that most of the tumour is well differentiated (grade II) but the least differentiated is grade IV.
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