Breast Cancer: an overview
VOL: 96, ISSUE: 47, PAGE NO: 34
Victoria Harmer, RN, BSc, AKC, is breast care nurse specialist at St Mary's Hospital, LondonOf every one thousand women in the UK, 15 will be diagnosed with breast cancer before the age of 50 and many will die, accounting for one fifth of all deaths in women aged 40-50 (McPherson et al, 2000). However, the incidence is higher among women aged over 60. One woman in 12 will develop breast cancer at some time in her life. While only about 200 new cases of breast cancer are diagnosed in men each year in the UK, of these 90 will die.
Almost all breast cancers arise from the lining of the milk ducts (ductal carcinoma) or milk lobules (lobular carcinoma)(Fig 1). Mucinous carcinoma, tubular carcinoma and typical medullary carcinoma are rarer and tend to be less severe. In-situ cancers
These occur when the cancer cells have not yet broken through the lining of the milk ducts or lobules, for example ductal carcinoma in situ. The malignant cells are totally contained by the boundaries of the milk duct and their surgical removal is the usual treatment - if left untreated in-situ tumours can progress to invasive breast cancer. It is not known how long this takes or what proportion of cancers do become invasive - although some analyses suggest up to 40% (Baum et al, 1995). Invasive cancer
This occurs when the cancer cells spread through the walls of the ducts and lobules into the surrounding tissue. From there they may invade the local blood supply and the lymphatic system. Characteristics of breast cancers
Biological characteristics can provide clues as to how aggressive the cancer is likely to be, including its potential to spread. It is often the case that breast cancer cells have spread around the patient's body long before a diagnosis is made. However, whether these cells ever give rise to metastatic disease depends upon certain biological characteristics of the tumour, such as the hormone-receptor status. Some breast cancer tumours are stimulated by oestrogen and progesterone and are known as oestrogen receptor and/or progesterone receptor positive. These hormones latch on to the cancer cells and encourage them to grow. Anti-hormone drugs, aimed at blocking the pathway of stimulation by either inhibiting the secretion of oestrogen or by blocking the oestrogen receptor, would therefore be recommended in these cases. Many biological factors have been shown to reflect tumour activity. CerbB2 (Her2neu) is a cell-surface ligand, overexpression of which seems to drive the cell cycle thus stimulating cancer cells to divide aggressively. This finding has therapeutic implications since anti-Her2 therapy - the drug trastuzumab (Herceptin) - which blocks this function, has now been put into clinical practice. Tumour differentiation
The probability of a patient developing metastasic disease in the future correlates, to a degree, with tumour size, number of involved axillary nodes and tumour grade (Todd et al, 1987). Prognostic information can therefore be gained by grading the tumour. Degrees of nuclear differentiation and speed of cell division are graded I to III. A tumour whose cells are slow to divide would be grade I, thus a grade III tumour would have an aggressive nature and suggest a poorer prognosis, as would tumour cells identified in the lymphatic system or in the local blood supply. Once breast cancer has been diagnosed, it is important to assess the stage so that the most appropriate treatment can be established. There are two major staging classification systems for breast cancer: the Manchester Staging System (see Table 1 and figs 2-5) and the TNM System (tumour, nodes and metastases) (see Table 2). The Nottingham Prognostic Index
Although it is impossible to prognosticate exactly, in any individual patient's case, the Nottingham Prognostic Index has been devised to try to do this. Retrospectively, combinations of prognostic factors have been derived as a more sophisticated aid to choosing or avoiding adjuvant therapy. The Nottingham Prognostic Index incorporates tumour size node status, and histological grade. If the lymph nodes are not involved then they are stage 1, if one to three nodes are involved then it is called stage 2, and if four or more nodes are involved, the stage is 3. The Nottingham Prognostic Index = 0.2 times size + lymph node stage + grade. (This will identify three prognostic groups). Genetics and family history
The high prevalence of breast cancer, with one in 12 women in the UK expected to develop it during their lifetime, means it can sometimes appear to run in families. However, the majority of human cancers occur sporadically and are caused by mutations accumulated in cells during a lifetime. Specialists estimate only 5-10% of female breast cancers in Western countries are due to a genetic predisposition. However, 10-20% of male breast cancers have a genetic link, highlighting the need for genetic counselling in men with strong family histories of the disease. Genetic breast cancer is transmitted through either sex, and within this group about 40% of families with several cases of breast cancer are due to predisposition by the BRCA 1 gene. A further 40% of breast cancer families carry a second breast cancer susceptibility gene, BRCA 2 (Cancer Research Campaign, 1994). Some family members may pass on the abnormal gene without developing cancer themselves. These inherited types of breast cancer tend to develop well before the age of 65, with most occurring in women in their 30s and 40s. A woman has a greater than two-fold risk of breast cancer if she has a first-degree relative (daughter, sister or mother) who developed the disease before the age of 50. The younger the relative when she develops the disease the greater the risk. The risk increases between four and six times if two first-degree relatives have had the disease before age 50 (McPherson et al, 2000). In principle, now these genes have been discovered, it should be possible to identify the family members at risk. However the social, financial and ethical consequences must be considered. Identification should be carried out within the context of careful counselling by carers who are informed about genetic risk. While the causes of breast cancer are still unknown, certain factors are associated with an increased risk (Table 3).