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.