Breast cancer

Breast cancer is a common disease, particularly in postmenopausal women ( ). Each year, in the United Kingdom, there are approximately 40,000 new cases diagnosed and 14,000 deaths. Male breast cancers constitute up to 1% of all mammary malignancies and may include tissue beyond the areolar boundary.

Breast cancers arise within the epithelia of lobules or ducts. As they increase in size and become invasive, they often lead to a fibrous stromal tissue reaction. Breast lumps may be classified as benign or malignant masses. More advanced malignant breast lumps (carcinomas) may have the clinical signs of infiltrating adjacent structures, leading to a hard and irregular mass with skin-tethering, muscle fixation, skin infiltration or oedema of the overlying skin ( peau d’orange ). Standard radiological imaging investigations of the breast include mammography and ultrasonography. Mammography is useful in detecting the presence of malignant masses as a stellate opacity with architectural distortion of the surrounding parenchyma. Preinvasive breast cancer, e.g. ductal carcinoma in situ , may appear as microcalcifications on the mammogram. An ultrasound scan of the breast is helpful to distinguish solid from cystic (fluid-filled) masses, and can also aid in the distinction of breast cancer from benign lumps by the different attenuation characteristics of the ultrasound waves and blood-flow patterns. Ultrasound may also be useful in guiding core biopsy.

A strong association between increased mammographic breast density and risk of breast cancer has been shown repeatedly. Breast density is assessed by mammograms where the appearance of the fibroglandular tissue is dense or white and the adipose tissue is less dense or grey. The fibroglandular tissue is comprised of epithelial cells, fibroblasts and connective tissue. Several scales of categorization of breast density have been devised. Wolfe was the first to introduce mammographic categorization of four mammographic patterns ( , ). Since then, in an effort to increase reproducibility of assessment of mammographic density, a number of methods have been devised comprising five or six categories. By the 1990s computerized measurements of mammograms were developed to calculate both total and percentage mammographic density. The computerized method has also been shown to be predictive of breast cancer risk. In general, there is high reproducibility and consistency between the scales, especially identification of women with high mammographic density ( ). Mammographic density appears to be influenced by a number of factors, including somatotype, BMI at 18 years of age, history of biopsy-confirmed benign breast disease (for both pre- and postmenopausal women) and hormone replacement therapy. It should be noted that premenopausal women’s breasts are more mammographically dense due to the increased fraction of glandular and collagenous tissue present prior to postmenopausal involution. Given that the majority of breast malignancies are also radio-dense, this limits the effectiveness (as measured by the reduction in breast cancer mortality) of mammographic screening in premenopausal women. Breast cancer rates increase in 40- to 49-year-old women compared to those less than 40 years of age. These statistics may prompt clinicians to consider screening high-risk women and also incorporate supplementary imaging such as ultrasound or magnetic resonance imaging in those with high breast density.

Magnetic resonance imaging (MRI) is useful in diagnosis, particularly in women with younger, denser breasts, achieving higher sensitivity of breast cancer detection but with lower specificity. A cytological diagnosis of a breast lump can be achieved using fine-needle aspiration (FNA) to evaluate the cellular component of a lump. FNA is also useful to drain symptomatic breast cysts. A wide-bore needle biopsy is a procedure performed under local anaesthetic to obtain several pieces of specimen for a histological diagnosis with the tissue architecture maintained. This permits distinction between in situ and invasive cancer, and provides an indication of tumour subtype by evaluation of the pathological characteristics. Vacuum-assisted mammotome biopsies based on the wide-bore needle enable some benign and indeterminate lesions to be excised for full histological analysis and, in some patients, can avoid the need for conventional open surgery.

If a breast lump has to be surgically removed, the incision should be based, whenever possible, in the relaxed skin tension lines, for the best cosmetic results. In women with sizeable malignant lesions in whom breast conservation surgery is to be attempted, the skin incision should be planned with consideration of the possible requirement for a subsequent mastectomy if the margins of excision are incompletely excised by pathological criteria ( ). Most women with single breast cancers of up to 4 cm in diameter are treated by breast conservation rather than mastectomy. This is a combination of surgery (tumour excision and sentinel node biopsy or clearance) together with external beam radiotherapy to minimize the risk of local recurrence. Patients with larger tumours are likely to be treated by mastectomy with axillary lymph node clearance. Neo-adjuvant endocrine or chemotherapy treatment prior to surgery may improve operability to allow breast conservation surgery of larger tumours.

During axillary dissection to clear the axillary lymph nodes, the long thoracic nerve (to serratus anterior), the thoracodorsal vessels, the thoracodorsal nerve (to latissimus dorsi), and the medial and lateral pectoral nerves are all identified and carefully preserved. The boundaries of the axillary dissection are the long thoracic nerve medially, the thoracodorsal vascular pedicle laterally and the axillary vein superiorly. The posterior limit of the dissection is the anterior (ventral) surface of subscapularis. The superomedial limit of a level 1 axillary dissection extends to the lateral (inferolateral) border of pectoralis minor at the apex of the axilla; a level 2 dissection extends to the medial (superomedial) border of pectoralis minor; and a level 3 dissection extends beyond the medial border until it reaches the point where the axilla is limited by the first rib (the latter is easily distinguished by its flat superior surface, easily palpable at surgery). Failure to preserve the long thoracic nerve will result in lifting of the medial border of the scapula (winging) from the posterior thoracic wall and a reduced scapula protraction. The intercostobrachial nerve is often sacrificed in an axillary lymph node clearance operation, and this may result in anaesthesia of a narrow strip of skin along the upper medial border of the ipsilateral arm.