Human breast tumours were analyzed with polymorphic microsatellite markers specific to chromosome 3p. Allelic imbalance (AI) was observed in 34% of the tumours. Microsatellite markers from two regions showed higher percentage of imbalance suggesting the presence of tumour suppressor genes or genes important for malignancy. Microsatellite instability was also found, implying errors in DNA replication. No significant correlation was found between AI and conventional prognostic variables. However, a striking correlation was found between AI and tumour S-phase fraction; AI was also significantly correlated with low steroid receptor content. A multivariate model including prognostic variables, showed that AI was without exception a significant prognostic variable; patients having tumours with AI had approximately a four-fold increase in relative risk of death. We conclude that screening for 3p deletions gives prognostic information and further investigations should reveal whether this finding could assist in treatment of the disease.

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