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Development of Cancer
Cell changes
Malignant changes occur over time. A normal or pre-malignant cell demonstrates normal anatomy and physiology. Neoplastic (new growth) or dysplastic (uncontrolled growth) changes are abnormal but not yet cancerous. When an abnormal cell invades tissue it can then be considered malignant, as in a malignant neoplasm.
We used to think that cancer developed in a predictable, progressive manner. Local disease led to regional lymph nodes and finally to metastasis. In response to this medicine responded with increasingly radical procedures to halt the progression of disease.
It is now understood that local disease extension, regional lymph node involvement and metastasis develop at unpredictable points in time. Cancer can spread before it is detectable locally or regionally, it is possible to have node negative metastatic disease (no disease in regional lymph nodes but evidence of more distant spread).
Disease detection
The threshold of clinical detection of a tumour is 1 cm = 1g = 1billion cells. Even radiographically evident tumours of 3-5 mm still represent millions of cells.
The latent period before a tumour becomes clinically detectable is usually YEARS. By then the average doubling time is 2-3 months (range < 1 month (childhood cancers) to years (salivary gland tumours). By the time a solid tumor is clinically evident, it has already completed a major portion of its life cycle
Screening programmes are based on our threshold for detection. We can improve our screening by lowering our threshold for detection.
The detection of cancer is also complicated but the fact that signs and symptoms of cancer can be local, regional or distant.
Detection by screening or signs and symptoms occur long into the process of a developing malignancy and our efforts to diagnose, treat and support represent a short time in the life of a malignancy.
The lethal tumour burden is approximately 1 kg = 1 trillion cells - there is only a 3 log difference between earliest clinically detectable mass and the lethal tumour burden.
