**2. Clinical characteristics and classification of breast cancer**

#### **2.1. Classifying breast cancer**

Breast cancer classifications are largely explained by differences in tumor characteristics as determined by tumor appearance, histology, tumor marker expression (immunohistochemis‐ try) or receptor status, and gene expression profiles. Alone, or in combination, these aspects can influence treatment, response and prognosis.

#### *2.1.1. Histology*

Breast cancer represents many different histologies, however the majority (estimated to be more than 85%) of breast cancers are collectively derived from the epithelium lining in the ducts or lobes, and are classified as mammary ductal or lobular carcinoma [9]. Furthermore, this classification can be defined as *in situ* (meaning the proliferation of cancer cells within the epithelial tissue without invasion of the surrounding tissue) or *invasive* whereby the surround‐ ing tissue is affected [9]. Included in the histological description of breast cancer is the status of invasion to the perineural and/or lymphovascular space and the presence of such is associated with more aggressive disease [10].

#### *2.1.2. Grade*

Tumor grade is determined by comparing differentiation in normal and cancerous breast tissues. Normal cells in the breast become differentiated and acquire specific shapes and forms that reflect their function as part of the mammary system [9]. When cell division becomes uncontrolled, differentiation is lost. Breast cancers are either well differentiated (low grade), moderately differentiated (intermediate grade), or poorly differentiated (high grade) [9]. This progressive loss of features seen in normal breast cells is indicative of disease progression and poorly differentiated or high grade cancers have a worse prognosis than others [11].

#### *2.1.3. Stage*

for success in treating cancer and increasing cancer patient survival [6]. There is an urgent need to explore agents that will be effective in preventing and treating metastasis of breast tumors.

In general, cancer occurs when a normal cell accumulates genetic and/or epigenetic changes caused by the activation or amplification of oncogenes and/or the mutation or loss of tumor suppressor function, resulting in the ability to proliferate indefinitely [7]. While these specific alterations lead to the transformation of the normal cell and partly determine the characteri‐ zation of the tumor, the cell of origin and tumor (micro-) environment are also considered important factors contributing to tumor cell establishment, progression and therapeutic

Breast cancer classifications are largely explained by differences in tumor characteristics as determined by tumor appearance, histology, tumor marker expression (immunohistochemis‐ try) or receptor status, and gene expression profiles. Alone, or in combination, these aspects

Breast cancer represents many different histologies, however the majority (estimated to be more than 85%) of breast cancers are collectively derived from the epithelium lining in the ducts or lobes, and are classified as mammary ductal or lobular carcinoma [9]. Furthermore, this classification can be defined as *in situ* (meaning the proliferation of cancer cells within the epithelial tissue without invasion of the surrounding tissue) or *invasive* whereby the surround‐ ing tissue is affected [9]. Included in the histological description of breast cancer is the status of invasion to the perineural and/or lymphovascular space and the presence of such is

Tumor grade is determined by comparing differentiation in normal and cancerous breast tissues. Normal cells in the breast become differentiated and acquire specific shapes and forms that reflect their function as part of the mammary system [9]. When cell division becomes uncontrolled, differentiation is lost. Breast cancers are either well differentiated (low grade), moderately differentiated (intermediate grade), or poorly differentiated (high grade) [9]. This progressive loss of features seen in normal breast cells is indicative of disease progression and

poorly differentiated or high grade cancers have a worse prognosis than others [11].

**2. Clinical characteristics and classification of breast cancer**

**1.2. The biology of breast cancer**

346 Using Old Solutions to New Problems - Natural Drug Discovery in the 21st Century

**2.1. Classifying breast cancer**

can influence treatment, response and prognosis.

associated with more aggressive disease [10].

resistance [8].

*2.1.1. Histology*

*2.1.2. Grade*

Between 1943 and 1952, Pierre Denoix devised the TNM staging systems for all solid tumors to classify the progression of cancer [12]; the acronym can be explained by the fact that this model utilizes the size and extension of the primary tumor (T), its spread to the lymph nodes (N), and the presence of metastases (M). Although it is not utilized for all cancers (i.e.: brain and spinal cord cancer), the TNM system has progressed to the 7th textbook edition (TNM Classification of Malignant Tumors) [12] and remains the major system by which breast cancer is staged. An increase in stage number is based on larger tumor size, nodal spread (in particular, the sentinel node\*) and metastasis and is positively correlated with a worse prognosis [13, 14].

\* Certain cancers spread in a predictable manner, from the site of origin to nearby lymph nodes (lymph glands) and then to other parts of the body. The very first draining lymph node is termed the "sentinel node" and is important in the sentinel lymph node biopsy (SLNB) technique utilized to stage the spread of certain types of cancer. The absence of cancer within the sentinel lymph node indicates that there is a high likelihood that the cancer has not spread to any other area of the body. Lymph node metastasis is considered one of the most important predictive signs in breast cancer, and thus can serve to guide the surgeon/oncologist to the appropriate therapy.

#### **2.2. Receptor status and gene expression profiles**

Recent progress in molecular technologies has led to distinct breast cancer categories and five distinct tumor types and a normal breast-like group have been identified to date based on gene expression profiling [15], as summarized in Table 1.


Positive (+ve), negative (−ve), estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptors (EGFR) 1 and 2 (Her 1 and 2) and cytokeratin 5, 6 (CK5,6).

**Table 1.** Distinct Molecular Tumor Categories of Breast Cancer and their Receptor Status

However, most investigators use the presence (+) or absence (-) of immunohistochemical (IHS) markers or receptor combinations that are expressed by neoplastic cells. In this manner, distinct tumor categories to-date are identified by the expression of estrogen receptors (ER), progesterone receptors (PR), human epidermal growth factor receptors (EGFR) 1 and 2 (Her 1 and 2) and cytokeratin 5, 6 (CK5,6) [15-19, 23-25]. Generally, molecular sub-types correspond to IHC receptor status [26]. These subtypes are of great clinical and research importance as they are utilized to administer and target therapeutic regimes based on predictions of response. Furthermore, these subtypes have been shown to display a wide variety of responses to different treatments [27-30] and are associated with other clinical outcomes, such as patient relapse and overall survival. The most favorable outcomes are noted for the luminal A subtype, which are hormone sensitive [31]. The Her2+ and basal subtypes are noted as more aggressive and have fewer therapeutic options [31-33]. The normal-like and claudin-low are unclassified (negative for all major receptors), and associated with poor prognosis [20-22, 30, 34]. Several small studies support the concept that molecular subtype and tumor receptor status may change during ordinary disease progression and a major study completed by MacFarlane *et al*. in 2008 revealed that 21% of relapsed tumors had changes in either ER/PR or HER2 receptor status [35]. This significant proportion led the author to suggest that biopsies of relapsed/ metastatic breast cancers should be performed routinely. This also should be an important consideration in research. In summary, treatment options considered effective in primary stage cancer may no longer be optimal in later stages of the disease, including relapses and metastasis as determined by the current classification scheme.

#### **2.3. Other classification approaches**

Other breast cancer classification approaches are also used to assist in both prognostic and treatment decisions. These include computer models that are based on a combination of several factors and offer individual survival predictions and calculations of treatment benefits [36]. For example, patients undergoing systemic adjuvant therapy can determine optimal treatment through the commercially available computer model *Adjuvant* which has been successfully validated in several cohorts, including the United States and Canada [36, 37]. Other useful classification tools utilized for breast cancer treatment choices include prognostic assessments (such as USC/Van Nuys prognostic index (VNPI)) and general comorbidity assessments [38, 39]. Also consider the case of familial breast cancer (genetic classification) whereby a patient may opt to undergo preventative measures such as mastectomy. Additionally, immunohisto‐ chemistry testing, other than those mentioned earlier, continue to prove favorable as prog‐ nostic markers across various molecular subtypes [40]. For example, in human breast cancer epithelial cell proliferation is considered a significant prognostic marker [41] and could possibly be used as a prediction tool to measure different hormone treatment related risks [42]. Therefore, the immunohistochemical marker, Ki67 (a nuclear protein expressed by cells in all active phases of the cycle except for quiescent or resting cells) is utilized frequently to evaluate proliferation [43]. Such labeling indicates a significant association with higher carcinoma grade, clinical response to endocrine therapy, higher risk of relapse, and worse survival in patients with early breast cancer [44].
