**3. Immune response in relation to invasive and in situ breast cancer**

Breast cancer, both the *in situ* and invasive forms, is an ideal target for vaccine therapy since this disease creates a significant public health burden. There is potential for vaccines to inhibit the progression of in situ disease into invasive cancer. The ultimate goal would be to prevent the formation of breast cancer altogether. Central to success of using immunotherapy to treat breast cancer is that breast tumors have already been established to be relatively immunogenic and the growing tumors are subject to immunosurveillance. Tumor antigens that are over-expressed or mutated in breast cancer cells initiate the development of a tumor-specific adaptive immune response [23, 37, 38]. T-cells that recognize these antigens have been isolated from breast cancer patients [39, 40]. As further evidence that the cell-mediated immune reaction has an important role in breast cancer development and clinical outcome, lymphocyte infiltration has been shown to be associated with improved survival in breast cancer patients [41]. Recent data by Mahmoud *et al*  confirmed that the presence of an efficient T-cell-mediated immune response is associated with breast cancer outcomes [42]. This study, a retrospective review of immunohistochemical staining from nearly 2000 patients with invasive breast cancer who received standard surgical and adjuvant treatment revealed that a higher number of CD8+ T lymphocytes infiltrating the tumor of adjacent stroma was independently associated with longer survival in patients with invasive breast cancers.

In addition to being immunogenic, other aspects of breast cancer make it a good model for the development of a high-impact cancer vaccine, especially for patients with early stage disease. First, solid tumor cancer vaccines have had limited success when used to treat advanced or metastatic disease [43]. Breast cancer is most frequently treated with surgery and radiation therapy, which greatly decreases the disease burden, even in advanced cases. This tumor debulking provides a greater potential for disease eradication by competent immune cells. Second, the typical slow growing nature of most breast cancers allows for the expansion of immune cells over time with repeated vaccine boosters. Therefore, effective levels of active and immune competent cells can be achieved before the disease becomes systemic.

Although most cancer vaccines have been developed to treat metastatic and systemic disease, there are a number of theoretical benefits to instead delivering vaccine therapy to patients with limited, microscopic cancer burden (as neoadjuvant therapy) in the absence of bulky disease. For instance, immune-competent patients would be able to produce a significant response comprised of antigen-competent T-cells that can rapidly expand when

Targeting Molecular Pathways

survivin [56-58].

**4.1 The EGF receptor family** 

**4.2 HER-1, HER-3, HER-4** 

for Prevention of High Risk Breast Cancer: A Model for Cancer Prevention 137

during surgical excision and could also prevent the risk of subsequent recurrence. In general, DCIS patients are often otherwise healthy and are therefore able to mount an immune response to vaccination. The long latency period between the diagnosis of *in situ* disease and the development of invasive breast cancer, as well as the minimal disease burden of DCIS, provides an ideal therapeutic window to administer preventative vaccines. This strategy of treating early disease is applicable to early invasive breast cancer as well as to other cancers with indolent courses or those that are diagnosed in early stages, such as

The selection of an appropriate target tumor antigen is paramount to the success of any cancer vaccine. The ideal vaccine would stimulate a significant immune response without causing autoimmunity and without a detrimental side effect profile. One strategy to avoid autoimmunity and to enhance the specificity of the vaccine is to target tumor antigens that are overexpressed in cancer cells but have minimal expression in normal cells. As mentioned in a previous section, one challenge to targeting oncogenic molecules is that these tumor associated antigens are usually only weakly immunogenic and are therefore capable of evading the immune response, or the immune system can immunoedit the tumors leaving behind antigen negative tumor cells. Many of the breast cancer tumor antigens are also overexpressed in other cancers of epithelial cell origin (colon cancer and ovarian cancer). Previously targeted peptides in the experimental production of vaccines against breast cancer include Mucin (MUC)-1, Her-2, carcinoembryonic antigen (CEA), and

The epidermal growth factor receptor (EGFR) family is a group of four related transmembrane receptor tyrosine kinases that have been implicated in the development of a multiple solid malignancies and have subsequently been targeted in a variety of novel therapeutics [59]. The EGFR family consists of HER-1 (also known as ERBB1), HER-2 (ERBB2), HER-3 (ERBB3) and HER-4 (ERBB4). These receptors bind 13 different ligands and form a number of different dimers between the family members. Ligand binding and dimerazation initiates various intracellular signaling pathways that affect numerous cellular processes involved in cell survival and proliferation. The oncogenic effects of the EGFR

HER-1 is a non-tissue specific peptide that has been implicated in the oncogenesis of multiple malignancies including breast, colorectal, pancreatic adenocarcinoma, brain glioma multiforme and non-small cell lung cancer [60]. The Food and Drug Administration (FDA) recently approved the use of a novel HER-1 directed tyrosine kinase inhibitor, erlotinab, in conjunction with other established medications for the treatment of advanced pancreatic and non-small cell lung cancers [61]. In addition, cetuximab is an anti-HER-1 monoclonal antibody that has been approved to treat patients with advanced colorectal cancer [62]. Although no anti-tumor vaccines have been formulated that are directed against HER-1, it is a feasible possibility to target this protein in order to develop an anti-HER-1 T cell response.

proteins result from amplification, over expression or mutation [60]. Refer to Fig. 1.

prostate and colon cancers, chronic leukemia and lymphomas [48, 55].

**4. Selection of a tumor antigen target** 

presented with low antigen levels of early disease or early recurrence [44]. In addition, patients with early stage breast cancer do not require aggressive adjuvant therapy. The immune response in vaccinated patients with early stage cancers will not be compromised by the limitations of these cytotoxic treatments, most importantly the long-term reductions in functioning B and T lymphocytes [45-47]. There has therefore been a shift in the field of immunotherapy towards the treatment of patients with minimal disease and the prevention breast cancer formation.
