PROGNOSTIC VALUE OF MIB-1 IN NEUROENDOCRINE TUMOURS OF THE LUNG

The spectrum of neuroendocrine lung tumours ranges from highly aggressive small cell carcinomas (SCLC) to carcinoid tumours (CD) of low malignant potential. Between these two extremes, the ‘well‐differentiated neuroendocrine carcinomas’ (WDNEC) form a transitional group with uncertain biological behaviour. This study investigated the prognostic value of the proliferation marker MIB‐1 (paraffin Ki‐67) in 59 neuroendocrine lung tumours (32 SCLC, 13 WDNEC, 14 CD) by immunostaining of routinely processed paraffin sections. Morphometric evaluation was done by semi‐automatic image analysis. The results were compared with survival data (mean follow‐up: 42 months). The proliferation rates of the tumours as determined by MIB‐1 immunoreactivity (MIB‐1‐PR) were significantly different between the tumour types (SCLC>WDNEC>CD) and showed a strong inverse correlation with survival time. In CD, the percentage of MIB‐1‐labelled nuclei never exceeded 1·1 per cent; higher values would therefore favour the diagnosis of WDNEC over that of CD. Among WDNEC, MIB‐1 was able to differentiate a subgroup with excellent prognosis (MIB‐1‐PR: 0·3–3·4 per cent) from another subgroup with a death rate of 50 per cent (MIB‐1‐PR: 7·3–20·3 per cent). Within each tumour type, all patients without distant metastases at diagnosis survived when MIB‐1‐PR was ⩽9·4 per cent, suggesting a potential threshold for prognosis. Although the status of metastases was the dominant prognostic factor in these neoplasms, MIB‐1 was able to provide additional prognostic information allowing the definition of prognostically different subgroups of patients. In conclusion, MIB‐1 and the status of metastases are complementary prognostic indicators and are best used in combination to characterize the biological behaviour of neuroendocrine lung tumours.