Apoptosis in breast lesions
|Vakkala née Mustonen, Merja1
1University of Oulu, Faculty of Medicine, Department of Pathology
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|Academic Dissertation to be presented with the assent of the Faculty of Medicine, University of Oulu, for public discussion in the Auditorium of the Department of Pharmocology, on May 26th, 2000, at 12.15 noon
Docent Päivi Heikkilä
Professor Veli-Matti Kosma
In this work the extent of apoptosis was studied in a set of 504 benign and malignant breast lesions to elucidate its role in breast tumor development and progression. Also the correlation of apoptosis with estrogen and progesterone receptor positivity, cell proliferation and patients ’ prognosis was studied. The breast lesions were also analyzed immunohistochemically with antibodies to apoptosis regulating proteins bcl-2 and bax, and caspases 3, 6 and 8. In addition, the immunohistochemical expression of NO• synthesizing enzyme iNOS in relation to apoptosis and angiogenesis was studied. Furthermore, the expression of the antioxidative enzyme MnSOD was studied in relation to apoptosis and cell proliferation.
According to the results, the apoptotic index was lowest in benign breast lesions. It was higher in in situ carcinomas, where a gradual increase in the extent of apoptosis from grade I to III in situ carcinoma was seen. The apoptotic index in invasive carcinomas was higher than in in situ carcinomas, and also in invasive carcinomas there was a gradual increase in apoptosis from grade I to III carcinomas. The apoptotic index was highest in recurrent carcinomas.
Strong bcl-2 expression was usually found in benign breast lesions but the immunoreactivity decreased in in situ and invasive carcinomas. There was a significant inverse association between bcl-2 immunoreactivity and the extent of apoptosis. Low bcl-2 immunoreactivity also associated with estrogen- or progesterone receptor negativity. In contrast, bax expression did not show any significant association with apoptosis, hormone receptors or the histologic types of tumors. Strong cytoplasmic caspase 3, 6 and 8 immunoreactivity was found in most carcinomas. It was weaker in in situ carcinomas and only weak immunoreactivity could be seen in benign breast lesions. There was a significant association between the extent of apoptosis and caspase immunoreactivity.
iNOS expression was found in both tumor and stromal cells. iNOS expression in tumor cells was more frequently found in invasive than in in situ carcinomas. Its expression correlated significantly with a high apoptotic index and high vascularization of the lesion. There was significantly less MnSOD immunoreactivity in invasive breast carcinomas compared to in situ carcinomas or benign hyperplasias. MnSOD immunoreactivity did not associate with the extent of apoptosis, but there was a marginal inverse association between cell proliferation and MnSOD expression.
Increased apoptosis was significantly associated with a high cell proliferation, and inversely associated with a positive estrogen status. A high apoptotic index (< 0.50%) was associated with a decreased survival of the patients.
The results of this study show that apoptosis plays a decisive role in the development and progression of breast carcinoma. It is influenced not only by apoptosis regulating proteins, such as bcl-2 and caspases, but also by the estrogen receptor status. Apoptosis was also associated with iNOS positivity, the effect of which is mediated through increased NO• production. In line with the suggested role of MnSOD as a tumor suppressor gene, its expression was downregulated in invasive breast carcinoma. In conclusion, the association of apoptosis with patient survival in breast carcinoma may be secondary to its association with tumor cell proliferation and high tumor grade, not necessarily suggesting any causal association between apoptosis and survival.
Acta Universitatis Ouluensis. D, Medica
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