The stroma surrounding the malignant cells is important for the growth and spread of the malignant tumour. Recently, accumulating evidence suggests that the local inflammatory process, previously believed to be the host response against cancer, might actually contribute to the development of malignancy and the inflammatory response in the tumours has gained increased attention [1
]. In follicular lymphomas, gene expression analyses have shown that genes associated with infiltrating inflammatory cells are more important than the tumour cells themselves for predicting outcome [5
Tumour-associated eosinophilia has been observed in human cancers, sometimes with different results regarding their association with clinical outcome [6
Mast cells derive from a specific bone marrow progenitor cell and migrate into tissues where they mature depending on the microenvironmental conditions.
Mast cells may promote tumour development through many different ways. Mast cells could facilitate tumour angiogenesis through heparin-like molecules and heparin could further permit neovascularisation and metastases through its anti-clotting effects [12
]. Moreover, mast cells secrete histamine and growth factors, such as VEGF (vascular endothelial growth factor), PDGF (platelet derived growth factor), SCF (stem cell factor) and NGF (nerve growth factor). Mast cells are also rich in metalloproteases that contribute to the majority of proteolytic components necessary for tumour invasiveness [3
]. On the other hand, mast cells could also be detrimental to tumour growth by secreting several cytokines and proteolytic enzymes participating in inducing apoptosis of the malignant cells, such as IL-4 [13
]. The dual role of mast cells in inhibiting or promoting tumour growth needs to be further investigated [14
]. Few studies of stromal mast cells in invasive breast carcinomas have been done and two previous studies have indicated that many stromal mast cells are correlated to a favourable prognosis [15
]. Furthermore, in lymph nodes of women with breast cancer a higher number of mast cells were found in the non-involved axillary lymph nodes in those women with a better prognosis [18
]. In women with axillary lymph node metastasis more mast cells were found in the non-involved axillary lymph nodes [19
]. These findings might indicate a protective effect of mast cells, possibly exerting a cytotoxic effect on the tumour cells. However, the studies are still few and further investigations are needed in order to elucidate the precise role of mast cells in the tumourigenesis. Mast cells interact with eosinophils in bidirectional interactions and cytokine networks [20
]. Eosinophils may serve as a source of SCF which induces the growth of mast cells regulating their activation, degranulation and chemotaxis.
In Hodgkin lymphomas, many eosinophils in the tumours are correlated to an unfavourable prognosis [7
] and many mast cells have been associated with an adverse clinical outcome [21
]. Interactions between mast cells and eosinophils in Hodgkin lymphomas are attributed to the CD30L-CD30 interaction [22
Tumour infiltrating eosinophils have previously been investigated in colon carcinomas [6
] but little data is known about breast cancer. In colon cancer a high amount of stromal eosinophils have correlated to a better prognosis.
The aim of this study was to determine if the presence and amount of tumour infiltrating mast cells and eosinophils in breast cancer correlated to prognosis.