BMC Cancer (2001) 1:8 http://www.biomedcentral.com/1471-2407/1/8 Table 5: Overall breast cancer survival in relation to serum concentrations of organochlorines by estrogen receptor status. Organochlorines in quartiles (ng/mL) Estrogen receptor positive Cases/control Adjusted RR (95% CI)a p trendb Estrogen receptor negative Cases/controls Adjusted RR (95% CI) p trend HCB I II III IV Dieldrin I II III IV ΣPCB I II III IV p,p'-DDE I II III IV <206.50 206.50-269.75 269.75-335.75 >335.75 <12.01 12.01-28.30 28.30-57.11 >57.11 <811.11 811.11-1076.04 1076.04-1405.73 >1405.73 <741.04 741.04-1129.75 1129.75-1688.85 >1688.85 13/15 15/14 17/12 13/15 8/21 17/12 17/12 17/12 14/15 15/14 13/16 17/12 15/14 13/16 17/12 14/15 1.0 ref.c 0.7 (0.3-1.6) 1.1 (0.5-2.4) 1.1 (0.5-2.5) 1.0 3.4 (1.3-8.7) 2.6 (1.0-6.3) 2.2 (0.9-5.4) 1.0 1.5 (0.6-3.4) 1.0 (0.4-2.3) 2.5 (1.1-5.7) 1.0 0.7 (0.3-1.6) 1.0 (0.5-2.2) 1.0 (0.5-2.1) >0.20 >0.20 >0.20 >0.20 7/4 8/3 3/8 4/7 4/7 3/8 7/4 8/3 6/5 7/4 5/6 4/7 6/5 4/7 5/6 7/4 1.0 0.9 (0.3-3.1) 0.2 (0.0-1.2) 0.2 (0.1-1.7) 1.0 0.4 (0.1-3.1) 1.9 (0.5-7.8) 1.8 (0.3-5.5) 1.0 0.4 (0.1-1.6) 0.5 (0.1-2.2) 0.1 (0.0-5.6) 1.0 0.3 (0.0-2.0) 0.7 (0.1-3.7) 0.3 (0.1-2.1) 0.03 0.06 0.02 >0.20 a Relative risk of dying, 95% confidence interval, adjusted for age at diagnosis, metastatic lymph nodes, and tumor size; b two sided p-value for linear trend in RR's; c Reference category. Cases with missing information on confounders were excluded. Large tumors are more frequently heterogeneous with respect to estrogen receptor expression than small tu- mors [39–42]. Consequently, a greater proportion of the large tumors will not exhibit estrogen reactivity at the time of diagnosis, although some part of it will be ERP. The tissue specimen obtained at the time of diagnosis may therefor not necessary reflect the original initiated breast cancer. These considerations may explain the present study's finding on dieldrin, as 27.3% of the ERN tumors among women in the highest exposure level had a diameter above 50 mm, while the corresponding figure for the ERP tumors was only 8.7%. Finally, it is possible that dieldrin is associated with a yet unidentified factor that modulates breast cancer risk. Whether exposure to estrogen related risk factors or or- ganochlorines with estrogenic potential results in devel- opment of an ERP breast cancer cannot be determined from current evidence, but deserves more attention in future larger studies. In the only study evaluating the influence of organochlo- rines on overall survival of breast cancer, an adverse ef- fect of dieldrin exposure was reported [24]. When the ER of the tumor was taken into account in the analysis of dieldrin, the relative risk of dying in the highest exposure level was elevated in both patients with ERP and ERN tu- mors, though not significantly. An adverse effect of diel- drin on survival of women with ERP tumors could be anticipated, as this compound is able to stimulate the growth of human estrogen-sensitive cells [2]. Another non-hormonal mechanism must lie behind the poorer prognosis of women with ERN tumors. Possibly, expo- sure to dieldrin may lead to development of a tumor with an increased inherent aggressiveness beyond what this study could take into account i.e. tumor size, degree of spread, and stage of disease. The significantly poorer prognosis observed for ΣPCB in women with ERP tumors is in accordance with the hormonal potential of some PCB congeners [1]. The breast cancer's responsiveness to estrogen is exploit- ed in endocrine surgery by removing the ovaries, and medically using drugs inhibiting the effects of estrogen on tumor cell growth. Worldwide results indicate that a 20% reduction in the five-year mortality is achieved by adjuvant therapy with tamoxifen in women over 50 years of age [6]. The use of tamoxifen has become more fre- quent and is not only reserved for postmenopausal pa- tients or patients with ERP tumors, because a proportion