Principles of cancer surgery
Cancer surgery has evolved over the decades from a radical ‘one size fits all’ approach to a patient-specific, cancer-specific direction, which means that surgeons rely on their multidisciplinary partners in the assessment of patients. As surgeons are frequently the first specialists involved with most solid tumours, familiarity with pre-operative imaging, pathological biopsy and patient-selection, careful surgical technique and staging are fundamental to the surgeon’s armamentarium.
Pre-operative imaging and TNM staging
Most solid tumours require adequate and site-specific imaging. This facilitates diagnosis and staging of the primary tumour and staging for distal metastases. Not all modalities are appropriate for all sites. For example mammography using the BIRADS system and ultrasound are used in breast cancers to assess a primary breast cancer. Meanwhile, an oesophageal cancer requires a CT and a low rectal cancer will be best assessed with MRI or endorectal ultrasound, whilst a thyroid cancer is best evaluated with neck ultrasound.
The goals of imaging the primary tumour are to assess tumour size, invasion into surrounding structures and operability. Imaging to stage a tumour aims at assessing nodal involvement and distal metastases.
The TNM staging system (American Joint Commission on Cancer AJCC) is devised for cancers to allow an assessment of T- tumour, N- nodal metastases and M- distal metastases. The goal of having a site-specific staging system is to estimate prognosis, facilitate treatment planning including the sequence of treatments and allow comparisons of treatment for different stages. Generally, a combination of different ‘T’, ‘N’, and ‘M’ allows the cancer to be grouped into stages. Stages I-IV usually depict a tumour in the following state: Stage 1- early and superficial cancer, Stage 2- locally advanced, Stage 3- regionally advanced with lymph node metastases and Stage 4- distant metastatic disease.
Despite suggestive imaging, a cancer is not diagnosed until histopathological biopsy. Biopsies where tissue (as opposed to cells) are provided to the pathologist increase the accuracy of the pre-operative diagnosis but may not always be feasible. Biopsies may be undertaken percutaneously -- for example, a core biopsy of the breast, fine needle aspiration of thyroid or endoscopically such as in gastric cancer or colon cancer.
A biopsy should confirm the tumour type, grade, may show lymphovascular invasion and in some cases, special immunohistochemical stains may be performed to assess hormone receptor status such as in breast cancer or flow cytometry may be performed to assess subtypes such as in lymphoma. Staging may also require a biopsy of draining lymph nodes.
The goals of a biopsy should be to provide a diagnosis without excessive morbidity to the patient. Areas that are not suitable for percutaneous biopsy include adrenal tumours or paraaortic masses.
Needle biopsy is not always adequate to aid treatment and occasionally incisional or excisional biopsies may be required. Lymphoma is a common tumour that may require a larger tissue sample to make the diagnosis.
Patient-selection and timing of surgery
One of the biggest challenges for the surgeon is to choose the correct surgery for the correct patient and with the tumour type and biology in mind. Although surgery removes a tumour and provides further pathological information to estimate prognosis and influence adjuvant therapies, the surgery cannot cause more morbidity than the cancer and must achieve surgical goals without compromising tumour biology.
When tumours are locally advanced, a neoadjuvant approach with chemotherapy, radiotherapy or targeted therapies may be important to ‘control’ the growth of a tumour, down-stage a tumour to render it operable, or because the impact of systemic disease risk may outweigh those of local control. Similarly, patients with metastatic disease may still require surgery to prevent complications of the primary tumour, such as bowel obstruction from a colon cancer.
The pre-operative multidisciplinary team including anaesthetists, cardiologists, dieticians, psychologists and social workers, and tumour-specific specialist nurses often assesses fitness for cancer surgery and the psychosocial impact of surgery.
Surgery of the primary tumour
The aims of any cancer surgery are to remove the cancer with an adequate margin of normal tissue with minimal morbidity. Clear margins have an impact on local control. Margin requirements differ according to the origin of the tumour and the functional impact must be considered.
Two examples of margins versus function/cosmesis include rectal cancer and breast cancer. A low rectal cancer requires an adequate margin above the anal sphincters to enable a primary anastomosis (anterior resection) that is not under tension and therefore at risk of anastomotic leak. As a cancer encroaches on the level of the sphincter muscles, the sphincters must be sacrificed in order achieve an adequate margin (abdominoperineal resection). In breast cancer, a wide local excision may be adequate for many breast cancers but if the result is poor cosmesis/ shape, a mastectomy may be a better operation to achieve a clear margin.
Surgery of the lymph node basin
Many solid tumours require removal of the draining lymph nodes for the purpose of staging and/or to achieve local control. Levels of prophylactic lymph nodes dissection vary according to tumour type and may increase surgical morbidity. Surgery in some tumours has become more conservative with the advent of sentinel node biopsy when lymph node metastases are not evident pre-operatively. Sentinel node biopsy is frequently used in breast cancer and melanoma. The aim of the sentinel node biopsy is to provide an assessment as a staging tool to predict prognosis and influence use of adjuvant therapies.
Surgery in metastatic disease and emergencies
Local control may become an issue in some patients with metastatic disease. Surgery may be undertaken in an elective or emergency setting in colorectal cancer to prevent or manage a bowel obstruction, to bypass a segment of small bowel involved with peritoneal disease or to place an endoscopic stent, for example in a metastatic cholangiocarcinoma or oesophageal cancer. In addition, in some tumour types, such as breast cancer, colorectal cancer or liver metastases, removal of the primary in a patient who has stable metastatic disease may improve prognosis and survival.
Surgery for prophylaxis
Cancer surgery includes managing patients at high risk of cancer in their lifetimes, usually due to an inherited mutation such as BRCA 1 or 2 or Lynch Syndrome. Although some medications, such as tamoxifen, may reduce risk of cancer, surgery in some organs reduces the risk of cancer in that site by about 95-97%. Organs removed in surgical prophylaxis include the breast/s, colon, stomach and thyroid.