The normal cell growth and division are largely under the control of a network of chemical and molecular signals that gives instructions to cells. Genetic alterations can disrupt the signaling process so that cells no longer grow and divide normally, or no longer die when they should. Alternations in two types of genes can contribute to the cancer process. Proto-oncogenes are normal genes that are involved in cell growth and division. Changes in these genes lead to the development of oncogenes, which can promote or allow excessive and continuous cell growth and division. Tumor suppressor genes are normal genes that slow down cell growth and division. When a tumor suppressor gene does not work properly, cells may be unable to stop growing and dividing, which leads to tumor growth.

The HER family of transmembrane receptors consists of four closely related members, including HER1 (also known as the epidermal growth factor receptor [EGFR]), HER2, HER3, HER4. These all are members of Erb B family of receptor tyrosine kinases. In general, they consist of extracellular ligands binding domain, a transmembrane domain, and an intracellular binding domain and an intracellular tyrosine kinase (TK) domain.

Monoclonal antibodies are a relatively new type of “targeted” cancer therapy. Normally, the body creates antibodies in response to an antigen entering the body, the antibodies attach to the antigen in order to mark the antigen for destruction by the body immune system. From 15% to 30% of breast cancers have been shown to express high levels of EGFR and HER2.⁶

Two main classes of agents have been developed that specifically target the EGFR.

1. Tyrosine kinase inhibitors (EGFR TKIs) - also known as Small Molecules.

These agents bind intracellularly. TKI s interacts with the enzyme tyrosine, which is active in a complex signaling system that is used by some cancers as a survival mechanism to allow them to grow out of control. These agents also effective in cases of endocrine resistance, as when breast cancers become resistant to endocrine therapy, growth signals through growth factor receptors and downstream kinases become dominant pathways. Thus, inhibition of these kinases may provide a basis to restore endocrine sensitivity. ⁷The examples of TKIs inhibitors are eg Gefitinib and Erlotinib etc.

Gefitinib- It is a signal Transduction inhibitor. This is an example of an orally active, selective EGFR tyrosine kinase inhibitor (EGFR-TK).⁶Gefitinib has demonstrated a dose dependant anti-proliferative effect on breast cancer cell. It has been found in experimental studies that ER- independent tumors were more sensitive to tyrosine kinase inhibition.

Since EGFR signaling appears to be up regulated in endocrine resistant breast cancers, tyrosine kinase inhibition may be effective in this clinical setting. ⁸Three phase III trials have examined the use of gefitinib in patients with advanced breast cancer. Clinical benefits (combined partial response and stable disease >6 months) was observed in 18 months. Pharmcodynamic studies have confirmed the ability of gefitinib to inhibit EGFR tyrosine kinase in skin and tumor biopsies. A higher response rate was observed in ER-positive, tamoxifen resistant patients. Gefitinib was generally well tolerated and showed evidence of antitumor activity. ^{9, 10, 11}

Baselga et al treated 31 patients with gefitinib and reported a 13% clinical benefit rate. ¹²Robertson et al reported a clinical benefit at 6 months in 5(26%) of 19 patients treated with gefitinib.¹³

Gutteridge et al. in a phase II study reported the effect of the expression of ER, EGFR, HER-2, and IGF- 1R in patients treated with gefitinib. Two groups of patients were recruited: an ER- positive tamoxifen – resistant (TAM- R) group and an ER- negative group. Pretreatment samples were taken for 35 patients, of which 13 were ER positive and 22 ER- negative. Although responders were seen in both groups, responses were more frequently observed in the ER- positive (82%) patients than the ER- negative (13%) patients. All responders expressed EGFR but a higher incidence of progressive disease, and shorter time to progression (TTP) were recorded in patients with high EGFR expression. HER-2 expression was similar in the ER – positive TAM-R patients (54.5%) and ER- negative patients (47.6%). In ER positive patients, high levels of HER-2 did not preclude a response to gefitinib and expression of IGF- IR did not predict response. ¹⁴

(2) Monoclonal antibodies (mAbs):- binds extracellulary to the receptor so avoid the ligands to bindings to the receptor thus blocks receptor dimerization, tyrosine kinase phosphorylation, and signal transduction.

An IgG₁, chimeric monoclonal antibody, competes with ligands binding to the EGFR ectodomain, resulting in an efficient blockage of the tumor promoting downstream signaling pathways. ⁶

Modi S et al in a phase I study evaluated synergistic effect of cetuximab with combination using cetuximab and paclitaxel in patients with metastatic breast cancer. Cetuximab weekly therapy and paclitaxel given 3 weekly, with dose escalation of cetuximab until the maximum tolerated dose was reached. ^{In three cohorts twelve patients were enrolled into three treatment cohorts. Of 10 patients evaluable for response, two had stable disease and eight had progression of disease, one patient out of three patients developed grade 3 skin toxicity. 15}

Trastuzumab- The recombinant, humanized MAb, trastuzumab (herceptin) is the first novel targeted therapy approved for routine clinical application in advanced breast cancer, targeted against the extracellular domain of HER 2. ¹⁶

Trastuzumab binds to HER 2 and inhibits signaling through other members of the HER family by inhibition of formation of the heterodimers important for potentiation of HER signaling, and this can result in decreased angiogenesis, increased apoptosis, and decreased proliferation. ^{16, 17}

Currently it is used as a standard treatment not only in the metastatic settings but also in the adjuvant setting. Furthermore, recent studies have revealed that trastuzumab plus chemotherapy in form of taxens and anthracycline dramatically increases the complete pathological response in the neoadjuvant setting, prompting the future use of this combination setting. ¹⁸

Cobleigh et al reported results of single agent trastuzumab in 222 women with metastatic breast cancer previously treated with one or two regimens for metastatic disease. All patients received the standard dose of 4 mg/kg IV weekly thereafter. An objective response rate of 15% was seen, with a median duration of response of 9.1 months, with exception of mild infusion reactions with the first dose and cardiac dysfunction in 4.7% of patients.¹⁹

Pegram et al evaluating in a trial chemotherapy with combination with trastuzumab, randomized 469 women with previously untreated metastatic breast cancer to chemotherapy alone vs chemotherapy plus trastuzumab. Patients received standard doses of doxorubicin and Cyclophosphamide unless they had received an anthracycline in the adjuvant setting. These patients received paclitaxel at a dose of 175 mg/m² every 3 weeks with or without trastuzumab. The addition of trastuzumab to chemotherapy resulted in an increased response rate (50% vs 32%, p<.001), a longer median duration of response (9.1 months vs 6.1 months<0.01), and prolonged overall survival (median 25.1 vs 20.3, p=.046). Toxicity was similar in the two groups, with the important exception of increased cardiac toxicity). With the combination of AC plus trastuzumab, 27% of patients had cardiac dysfunction compared with 8%of patients who received AC alone. The combination of paclitaxel and trastuzumab resulted in cardiac dysfunction in 13% of patients while only 1% of patients receiving paclitaxel alone had cardiac dysfunction. As a result of this trial, all patients with HER2 overexpressing metastatic breast cancer should receive trastuzumab in addition to their palliative chemotherapy, but anthracycline/trastuzumab combinations should be avoided outside of a clinical trial.²⁰

Vogel et al evaluated single agent trastuzumab in the first line setting in 114 women with metastatic breast cancer. All patient had tumors scored as 2+ or 3+ by IHC. Two different dose levels were evaluated, but no difference in outcome was observed for the higher dose compared with the standard dose. The objective response rate for the whole population was 26%, with 38% having clinical benefit (response or stable disease for 6 months). Roughly half of patients with a clinical benefit or response were free of disease progression at 1 year. Median survival was 24.5 months, which rivals the chemotherapy plus trastuzumab result from the pivotal trial with a similar population. ²¹

Latest data on the adjuvant use of trastuzumab highlighted by Perez, they provided an update on the clinical efficacy from the combined analysis of NSABP B31 and NCCTGN9831. Ongoing follow up of the adjuvant trastuzumab trials, in which patients received AC followed by paclitaxel, with or without the addition of trastuzumab, shows persistent and durable benefits. The difference in DFS through 4 years of follow up is 13% in absolute terms (73% without trastuzumab, 86% with trastuzumab) reflecting a 50% relative reduction in risk of recurrence. ²²

Lapatinib is a small molecular inhibitor of TK domain of both HER 1 and HER2. EGFR or HER2 expression through decreased phosphorylation of the TK domains of both receptors drives inhibition of growth and induction of apoptosis in breast cancer cell lines.¹⁶ Lapatinib has a significantly longer half life than gefitinib or erlotinib.²⁶ In a phase I b trial of lapatinib in EGFR and / or HER2 expressing cancers, sixty six patients were treated, including 30 patients with metastatic breast cancer. Four of the patients with metastatic breast cancer (13%) were believed to have stable disease at a median duration of therapy of 5 months. All 4 had progressed through prior trastuzumab. Ten patients (33%) were believed to have stable disease at a median duration of therapy of 5 months. All 10 had EGFR expression by IHC, and 8 of these 10 overexpressed HER2.²⁷

Brain metastases are a considerable cause of morbidity and mortality in patients with HER 2- positive metastatic breast cancer patients treated with trastuzumab. Lapatinib has been demonstrated to cross the blood – brain barrier, thereby offering the possibility of preventing or treating brain metastasis. ²⁸

Based on this hypothesis, Lin and colleagues examined the use of single agent Lapatinib in patients with HER-2 positive metastatic breast cancer who had brain metastasis that progressed on whole brain radiation and /or radiosurgery. Although the partial response rate was 5%, 42% of patients had stable disease lasting greater than 8 weeks. Using a complex volumetric assessment, 26% of patients were noted of at least 20%. Patients who had disease progression in the brain or systemically were offered enrollment in an extension study, in which they received Lapatinib and capecitabine at FDA- approved doses. Of note, 60% of patients had a reduction in brain volumetric tumor of at least 20%.²⁹

A phase III trial demonstrated that lapatinib plus capecitabine is superior to capecitabine alone in women with HER2 – positive advanced breast cancer that progressed after prior therapy including trastuzumab. Time to progression has been increased by addition of lapatinib and resulted in improved overall survival. ³⁰

In a neoadjuvant phase II study Cristofanilli M et al with paclitaxel monotherapy in combination with lapatinib in inflammatory advanced breast cancer, observed clinical response rate of 77% and a pCR of 17% were achieved in HER2 – positive tumors. Eighty percent of EGFR- positive patients exhibited a response. ³¹

It is now proved by the US Food and Drug Administration.³²

(2) Anti-angiogenesis compounds (Angiogenesis Inhibitors): VEGR and VEGF receptors

Anti angiogenesis drugs starve the cancer cells of blood that they need to survive and grow. Tumor cells, like normal cells, need an adequate blood supply in order to perform vital cellular functions. In fact, as cells multiply and grow in number and size, access to nutrients and blood supply becomes increasingly critical for their continued survival. Actively dividing tumors secrete special proteins that signal the surrounding areas to sprout new blood vessels. This new blood vessel formation is called angiogenesis, and the proteins that trigger this process are called proangiogenic factors. The main proangiogenic factor is VEGR, which stands for vascular endothelial growth factor. In essence, by secreting VEGR and other related proteins to stimulate new blood vessel growth, tumors support and feed themselves, allowing them to grow. The concept behind angiogenesis inhibition, then, is to thwart this process and thereby fight tumor progression. (Bevacizumab, sunitinib)

The p53 gene acts as a regulator of cell growth and DNA repair in normal cells, inactivation of the gene appears to lead to cancer. About 35% of breast cancer patients have p53 mutation, of which 88% are located within exons 5 to 8. ⁴¹ p53 mutation occur in 24.5% of the axillary node negative breast carcinomas and more frequently in cancer with HER2 amplification. ⁴²Intra tumoral administration of a nonreplicating adenoviral vector that contains the human wild type p53 combined with chemotherapy could increase the efficacy of primary systemic chemotherapy as measured by pathological complete response in the management of patients with locally advanced breast cancer. ⁶

In a prospective clinical trial II open label, 13 patients with locally advanced breast cancer were treated with six 3-week cycles of primary systemic therapy, which consisted of intra-tumoral injections of human wild type p53 (Ad5CMV-p53) for 2 consecutive days plus docetaxel and doxorubicin followed by surgery and concluded Ad5CMV-p53 combined with PST was safe, active and associated with local immune modulatory effects. The promising clinical activity of this combination deserves further investigation in randomized studies.⁴³