METASTATIC POTENTIAL OF SMALL AND MINIMALLY INVASIVE BREAST CARCINOMAS

Invasive ductal mammary carcinomas (IDC) of 1 cm in tumour size or les s account for less than 20% of all IDC. We have observed 167 such case s at our Institution between 1985 and 1989. These were divided into ca rcinomas with an extensive or predominant intraductal component (EIC o r PIC, being least 2x or 4x larger than the invasive component; 90) an d compared statistically with the control group (no EIC or PIC; 77) fo r known prognostic factors and for their metastatic behaviour. Lymph n odes were step sectioned in order to detect occult micrometastases. Th e median follow up time was 62.6 months. Lymph node metastases were se en in 10% of pT1a and 19% of pT1b cases. Significant differences were found when comparing the EIC/PIC group with the control group (pT1a: 1 1% vs. 0%, pT1b: 37% vs. 11% lymph node metastases). Also, axillary an d infraclavicular recurrence rates were higher for EIC/PIC carcinomas compared with other IDC of less than or equal to 1 cm (9.3% vs. 4.2%). This significantly adverse metastatic behaviour of the EIC/PIC tumour s may be in part due to the more frequent occurrence of multifocal tum ours in this group (in 43% vs. 6%), resulting in a greater tumour burd en. We conclude that the overall risk of lymph node metastasis is not negligible in carcinomas of 1 cm or less in diameter with the risk bei ng more than doubled for carcinomas with an intraductal component exce eding the invasive tumour by a factor of two. These differences were r elevant only to regional metastases; the risk for distant metastasis a nd survival was identical after 5 years.