SOFT-TISSUE SARCOMA AFTER TREATMENT FOR BREAST-CANCER

In a register study all women in the West of Sweden Health Care Region with a breast cancer diagnosed between 1960 and 1980 (n = 13 490) wer e followed up in the Swedish Cancer Register to the end of 1988 for la ter occurrence of a soft tissue sarcoma (STS). Nineteen sarcomas were reported, whereas 8.7 were expected and the relative risk (RR) was 2.2 (CI 95% 1.3-3.4), The absolute risk was 1.7/10(4) person years (PY) i n comparison with 0.8 expected, To obtain a more detailed analysis of the associations between arm lymphoedema, radiotherapy and STS develop ment, and to control the quality of the register data, a case control study was also performed. Clinical records from the different hospital s in the region were collected for all the 19 cases as well as for thr ee selected controls per case. The histopathology of the cases were re viewed, and one of the cases was reclassified as a malignant melanoma and excluded from further analysis. Thirteen of the cases were cluster ed around the treated breast area. To quantify the exposure to radioth erapy, the integral dose was estimated. The presence of lymphedema was included as a binary variable in the analysis. The exact conditional randomisation test indicated a significant correlation between the int egral dose and the development of an STS (p = 0.008) and this associat ion was still significant after stratification for arm oedema. A condi tional logistic regression analysis with STS as the dependent variable and the integral dose as the explanatory variable gave an odds ratio (OR) of 5.2/100 J (CI 95% 1.3-21.2), and if this regression was restri cted only to the STS developing in the radiation fields the OR was 3.2 /100 J (CI 95% 0.8-12.9). Thus, the excess of STS in this breast cance r cohort was very low (0.9/10(4) PY). However the integral dose correl ates well to the development of STS and can be useful in quantifying e ven small risks of secondary malignancies in the breast cancer populat ion.