Heme oxygenases (HOs) catalyze the oxidation of heme to the biologically active products carbon monoxide (CO), biliverdin, and ferrous iron. Two distinct variants of HOs have been described in humans and rodents, each encoded by a different gene: HO-2, which is constitutively expressed, and HO-1, which is potently induced in many cell types by heme, inflammatory cytokines, and oxidative stress-related factors.

The goal of this study was the prognostic evaluation of histology, mitotic rate, S-phase fraction (SPF) and expression of proliferative antigen Ki67 and p53 protein in phyllodes tumor of the breast. The study was performed in the group of 118 patients with phyllodes tumor treated by surgery from 1952 to 1998. Mitotic rate was assessed on the representative histological specimens. Expressions of Ki67 and p53 were evaluated by immunohistochemistry on a section from the corresponding paraffin blocks which were also used for flow cytometric DNA evaluation. Histologically, 52 tumors were benign (LGM), 24 borderline malignancies (BM) while among 42 malignant tumors, 20 were monomorphous (HGM) and the remaining 22 revealed heterologic elements (HGH). Tumor recurrencies occurred in 17 patients, predominantly during the first three years after surgery, and 13 patients died of the tumor (1 BM, 12 both malignant variants). Multivariate analysis demonstrated mitotic rate, SPF and p53 expression as independent prognostic parameters for the disease-free survival. Histological tumor type and expression of Ki67 influenced independently the overall survival. In conclusion, the histological type of tumor phyllodes forms the basis for the prognosis of clinical outcome, but the indicators of the proliferative activity, especially Ki67 index, are valuable prognostic factors among patients with malignant variant of phyllodes tumor of the breast. Expression of the p53 protein in tumor cells could be also useful when the percentage of cells and intensity of expression are considered.

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Heme oxygenase-1 (HO-1) is an antioxidative and cytoprotective enzyme, which may protect neoplastic cells against anticancer therapies, thereby promoting the progression of growing tumors. Our aim was to investigate the role of HO-1 in cancer induction. Experiments were performed in HO-1+/+, HO-1+/−, and HO-1−/− mice subjected to chemical induction of squamous cell carcinoma with 7,12-dimethylbenz[a]anthracene and phorbol 12-myristate 13-acetate. Measurements of cytoprotective genes in the livers evidenced systemic oxidative stress in the mice of all the HO-1 genotypes. Carcinogen-induced lesions appeared earlier in HO-1−/− and HO-1+/− than in wild-type animals. They also contained much higher concentrations of vascular endothelial growth factor and keratinocyte chemoattractant, but lower levels of tumor necrosis factor-α and interleukin-12. Furthermore, tumors grew much larger in HO-1 knockouts than in the other groups, which was accompanied by an increased rate of animal mortality. However, pathomorphological analysis indicated that HO-1−/− lesions were mainly large but benign papillomas. In contrast, in mice expressing HO-1, most lesions displayed dysplastic features and developed to invasive carcinoma. Thus, HO-1 may protect healthy tissues against carcinogen-induced injury, but in already growing tumors it seems to favor their progression toward more malignant forms.

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