Background: In about 50% of colorectal cancer cases, metastases are responsible for tumour-specific death. This study examines influences on survival after diagnosis of metastases and conclusions that can be drawn from the time pattern of a progressive disease course.
Methods: The background was provided by Munich Cancer Registry database (Germany). Population-based, good follow-up, high quality of clinical data, and results comparable to those of other cancer registries stand for validity of these data.
Results: Number of positive lymph nodes is the best prognostic factor. However, since metastasis may be initiated before diagnosis of the primary tumour, growth of the primary tumour and the metastases may be two autonomous processes. Thus survival following metastasis is almost unrelated to prognostic factors from the primary tumour, and median survival time after diagnosis of metastases is therefore almost comparable with 17 months. From the distribution of survival time after diagnosis of the primary tumour, the time from initiation of metastases to their diagnosis can be estimated at about 6 years. This means that metastases diagnosed synchronously with the primary tumour (M1) were initiated 6 years before detection of the primary tumour and also that metastases diagnosed during follow-up had already started before therapy of the primary tumour. In consequence, positive lymph nodes are an indicator but not a cause of metastases.
Conclusions: Specific time relations support the hypothesis that all metastases were initiated before diagnosis of the primary tumour. This hypothetic model has a high explanatory potential, also for evidence of the missing survival benefit from radical lymph node dissection.