Tumours in Iceland. 10. Malignant tumours of the female breast. A histological classification, laterality, survival and epidemiological considerations.

The Icelandic Cancer Registry has records of 1,720 cases of malignant tumours of the female breast diagnosed in 1,659 patients in the 30-year period 1955-1984. Of these, 1,658 tumours were invasive. Sufficient histological material existed for 1,666 malignant tumours to make it possible to classify them according to the criteria published by the WHO. The most frequent histological type was Ductal carcinoma: 1,064 neoplasms, or 64%. Second in frequency was Lobular carcinoma: 175 neoplasms, or 10%; third was Mucinous carcinoma: 115 neoplasms, or 7%; and fourth in frequency was Medullary carcinoma: 69 neoplasms, or 4%. The incidence of carcinoma of the breast increased by 74% from 37.0 per 100,000 per annum in 1955-59 to 64.4 per 100,000 in 1980-84. This increase in incidence affected all morphological types, but Lobular and Mucinous more than Ductal and Medullary. The survival times have improved with time. Unilateral tumours were 710 in the right and 837 in the left breast. Both breasts were involved 167 times (106 patients), and in 6 patients the side was not recorded. A second primary was more likely to develop when the first one was in the right breast. This study of malignant tumours of the breast is the tenth in a series of investigations into histological classification of tumours occurring in Iceland.