Introduction
A biopsy is indicated to confirm, support or eliminate the diagnostic probabilities for a mass that has been identified from physical examination, radiographic evaluation or laboratory data. When considered in conjunction with other aspects of the clinical investigation, the results of a biopsy can be used to determine the likely prognosis for the patient, and to guide optimal treatment options for the patient, including the extent of surgical resection that may be required, and the indication for neoadjuvant or adjuvant therapies.
Many hypothetical contraindications and concerns have been raised against performing a biopsy. The potential cost and apparent therapeutic delay associated with a biopsy procedure is a common concern; this is best countered by understanding what is to be gained by the biopsy in terms of improved patient management. While there are some situations when the results of a biopsy will not directly change patient management, there are many other examples where the biopsy result is vital to making informed decisions for the patient. "Unplanned" resection of a tumour can have devastating consequences for a patient, e.g., a formerly 'operable' lesion may become inoperable, or the patient may have to undergo a more extensive procedure (or combinations of treatments), which increases patient morbidity and client costs.
Making intelligent use of the variety of biopsy tools that are now available ensures the clinician can obtain a tissue biopsy without having to undertake a 'mini-surgical' exploration. This improves the efficiency of the procedure, thereby reducing the cost and inconvenience for the patient and owner.
The potential for encouraging seeding of metastatic cells during biopsy of a neoplastic mass is a problem perceived by many clients. The metastatic potential of a tumour is an inherent biologic state acquired by the tumour itself. Development of metastatic disease is a complex biological process, requiring an interplay between neoplastic cells, the host and the site where a cell has become lodged. Therefore, the biopsy procedure is unlikely to induce metastatic spread of the tumour. However, local invasion (or seeding) of a tumour along biopsy tracts is an important and recognized phenomenon (Robertson, Baxter 2011). The incidence of biopsy tract seeding for many human neoplasms varies with the type of neoplasm involved and may range from less than 1% for bone and soft-tissue biopsies, to up to 22% for mesothelioma. Although isolated reports of needle tract seeding exists in the veterinary literature, the overall incidence is unknown. The impact of biopsy tract seeding can be controlled by ensuring the biopsy site is taken from a site which can be completely removed should tumour excision be required subsequently.
Biopsy Techniques
There are several methods available to the clinician to obtain a biopsy from a mass. Clinical judgment must be used to decide which is the most appropriate and cost-effective sampling method to employ to ensure as much information about the mass is obtained as possible.
Cytology: Fine-Needle Aspirate
Diagnostic cytology is an extremely easy and cheap method for obtaining samples from a wide variety of masses and body cavity fluids. Superficial masses, which can be easily immobilised, are readily sampled. Deeper lesions (including liver, kidney, spleen, etc.) may be more safely aspirated in combination with ultrasound imaging modality.
Aspiration is so easily performed that it should be the first step in any diagnostic investigation of an abnormal mass/body cavity fluid. Impression smears should also be gained from a portion of gross tissue removed for incisional biopsy for in-house cytological examination. Being able to stain a slide, perform a preliminary examination of the smear and recognize the presence of clinically relevant cellular material in the specimen is a simple skill and ensures that any tissues submitted to the lab have a good prospect to yield a diagnosis. It is obviously better to recognize a sample is nondiagnostic before the animal leaves the hospital, rather than several days later when the pathology report is received.
Histopathology: Biopsy
Although cytology is the most expedient diagnostic method, it does not reveal architectural information about the cancer. Also, certain cancers may not exfoliate cells sufficiently to enable cytological examination. Architectural information is useful to establish the grade, which can provide a measure of the cancer's aggressiveness. The grade may influence the prognosis, and as a consequence, the treatment strategy. For this reason, a biopsy obtained from the tissue may be more beneficial and cost effective when the ultimate prognosis may bias the owner's choice of treatment, or may radically alter the cancer therapy (e.g., tumours on distal limbs, most soft-tissue sarcomas, periarticular tumours).
Incisional biopsy: Incisional biopsies can be taken with a scalpel, biopsy punches, needle core biopsy instruments, or trephines. Closed biopsies are taken without direct visualisation of the mass. They are most easily obtained using percutaneous needle-core biopsy instruments (e.g., Tru-cut needles or trephines). The biopsy instrument can be inserted into the tumour by direct palpation, or with ultrasound guidance. Biopsies can be obtained under local anaesthetic, or with sedation/anesthesia, depending on the temperament of the patient or the location of the tumour. Because only small sections of the tumour are obtained, multiple samples (minimum of 6 cores for Tru-Cut needles) should be obtained from different locations to improve the diagnostic yield. With good technique, percutaneous needle biopsy can provide reliable diagnostic information equivalent to a full surgical biopsy (Perry et al. 2012). Disadvantages of blind biopsy are that the biopsy instrument cannot be directed to the area of greatest interest (i.e., the biopsy is somewhat random), and haemorrhage (if it occurs) is difficult to control.
Open biopsies are taken under direct visualisation. This allows a biopsy to be obtained from a chosen area of the tumour, and control of haemorrhage is improved. Care should be taken not to widely open uninvolved tissue planes that could become contaminated with released tumour cells, making subsequent curative resection more complicated. Disadvantages of open biopsies are the increased cost, procedural time and potential discomfort to the animal.
Excisional biopsy: On occasion (e.g., for small or easily removed tumours where surgical planning is obvious and a cytological diagnosis has already been obtained), complete excision of the mass may be performed without an intervening 'histological' evaluation. Definitive diagnosis and treatment are therefore performed concurrently. Because knowledge about the tumour biology may be limited, determination of the appropriate surgical margin about the tumour will be based on empirical guidelines. The potential for under- or over-treatment of the mass is therefore a real concern with excisional biopsies.
Whenever complete excision of a mass has been attempted, it is important that histological examination of the resected margins is performed to ensure no tumour cells have been left behind. It is also important to realize the limitations of this 'margin' assessment. For a pathologist to accurately determine histologic margins from a 1-cm tumour resection, a pathologist would need to examine more than 4,000 sections. In most commercial veterinary laboratories, reporting is performed on just three to six sections. Therefore, to improve the accuracy of margin assessment, it falls to the surgeon to ensure that the tissue specimens submitted to the pathologist best reflect the tumour bed from which they were removed. The surgeon knows best which bits of the tissue "looked a bit odd" at surgery, or where margins were compromised by anatomical structures. Questionable edges can be "tagged" with suture material, or coloured inks can be used to paint lateral and deep margins of the excised tissue. This method can prevent the confusion of overlying tissue layers that may become distorted during fixing. Another option for improving the sensitivity of margin evaluation is for the surgeon to take a further section of tissue from the edges of the tissue remaining in the wound bed after excision. This tissue is submitted alongside the main tumour and is used for specific margin analysis. Microscopic evidence of neoplastic cells in this tissue more confidently predicts the presence of residual disease in the patient.
Utilising Biopsy Information for Surgical Planning
The intention of most surgeons when operating on cancer is to achieve a curative resection, leaving no trace of the tumour - "a clean margin." An incomplete resection ("dirty margin") is consistently associated with significantly reduced survival times. In their study on mast cell tumours, Michels et al. (2002) reported that all tumour-related deaths only occurred following local relapse of the tumour. Similar findings have been reported for a whole range of tumours, including mast cell tumours, soft-tissue sarcoma, lung tumours, etc. (Kuntz et al. 1997; Chase et al. 2009; Bray et al. 2011; Polton et al. 2008).
During the development of oncologic surgery over many decades, in both human and veterinary fields, the belief that "more must be better" has driven surgeons to take wider and wider excision margins, particularly when dealing with aggressive malignancies. Although extensive surgery may achieve local cure in many cases, it can result in significant morbidity. As we gain a greater understanding and interest in cancer management, these relatively dogmatic treatment strategies are justifiably being reviewed.
It would be helpful if a surgeon could accurately determine the local extent of an individual tumour before commencing surgery. We are still some way off being able to "visualise" the extent of an individual tumour's local infiltration, so for the moment we persist with broadly prescriptive advice. Currently, the best predictor we have of tumour behaviour is histological grade or other surrogates of aggression, such as tumour size, recent rapid growth or ulceration. Regrettably, more than 90 percent of soft-tissue sarcoma resections performed in general practice remain "unplanned," i.e., the surgeon had performed no prior investigations to determine the nature of the mass being removed (Bray et al. 2011). In that study, fine-needle aspirations were performed in 22 percent of cases, but this technique was mainly used to "rule out" mast cell tumour or lipoma. Thus, histological grade was determined in less than 4 percent of patients with soft-tissue sarcoma before surgery. It is clear that efforts to improve pre-surgical analysis of tumour biology before resection will enable a better prediction of surgical dose and patient outcome.
References
1. Bray J, Polton G, Whitbread T. Outcome of 490 cases of soft tissue sarcoma managed in first opinion practice. (Abstract); European Society Veterinary Oncology Annual Congress, Glasgow, UK; 2011.
2. Fulcher RP, Ludwig LL, Bergman PJ, et al. Evaluation of a two-centimeter lateral surgical margin for excision of grade I and grade II cutaneous mast cell tumors in dogs. J Am Vet Med Assoc. 2006;228(2):210–215.
3. Kamstock DA, Ehrhart EJ, Getzy DM, et al. Recommended guidelines for submission, trimming, margin evaluation, and reporting of tumor biopsy specimens in veterinary surgical pathology. Vet Pathol. 2011;48(1):19–31.
4. McSporran KD. Histologic grade predicts recurrence for marginally excised canine subcutaneous soft tissue sarcomas. Vet Pathol. 2009;46(5):928–933.
5. Michels GM, Knapp DW, DeNicola DB, et al. Prognosis following surgical excision of canine cutaneous mast cell tumors with histopathologically tumor-free versus nontumor-free margins: a retrospective study of 31 cases. J Am Anim Hosp Assoc. 2002;38(5):458–466.
6. Robertson EG, Baxter G. Tumour seeding following percutaneous needle biopsy: the real story! Clin Radiol. 2011;66:1007–1014.
7. Perry JA, Culp WT, Dailey DD, Eickhoff JC, Kamstock DA, Thamm DH. Diagnostic accuracy of pre-treatment biopsy for grading soft tissue sarcomas in dogs. Vet Comp Oncol. 2012.