Imagine this clinical scenario: a client brings in a four-year-old neutered male Pug with a 1cm cutaneous mass in the left flank region. The owner reports that the mass has been there for three months and has not changed in size. Cytology suggests a mast cell tumour (MCT). Blood work and an abdominal ultrasound are unremarkable.
You consider how large a surgical margin you would ideally use to excise the mass. Therefore, you decide to consult the literature to explore whether the extent of surgical margin affects the likelihood of local recurrence of Patnaik grade I or II cutaneous MCTs.
Eight papers were reviewed. Five were retrospective case series (Chu et al., 2020; Itoh et al., 2021; Pratschke et al., 2013; Saunders et al., 2020; Séguin et al., 2001). Two were prospective clinical trials (Fulcher et al., 2006; Milovancev et al., 2019) and one was a prospective case series (Simpson et al., 2004).
Sample sizes ranged from 16 to 68 animals with one or more Patnaik grade I or II (Kiupel low-grade or high-grade) tumours on the head, neck, trunk, flank, limb, inguinal region or prepuce and genital area. From 23 to 100 MCTs were excised. Cytology, histopathology and medical records were used for diagnosis. Adjuvant therapies (radiation and chemotherapy), neoadjuvant treatments (corticosteroids and antihistamines) and post-operative amputation were used.
The outcomes studied were local recurrence, completeness of excision, margin of excision, time of local recurrence, survival time and disease-free interval
The outcomes studied were local recurrence, completeness of excision, margin of excision, time of local recurrence, survival time and disease-free interval.
Limitations of the evidence
The overall quality of the evidence was low as it predominantly comprised retrospective observational studies, some of which had incomplete records, and there were no randomised prospective clinical trials. Most studies also had a small sample size.
Other limitations included:
- a lack of clear definitions for exact margins and local recurrence in relation to the original scar
- a lack of a control group
- a lack of randomisation
- the use of additional treatments
- a subjective, inconsistent and/or incomplete follow-up
The overall quality of the evidence was low as it predominantly comprised retrospective observational studies, some of which had incomplete records, and there were no randomised prospective clinical trials
Summary of findings
Séguin et al. (2001) used 2 to 3cm margins to remove MCTs and found 5 percent of tumours (3/60) recurred locally. This study had a small sample size and did not have separate groups for different excision margins. It included MCTs previously excised incompletely and used amputation, which precluded the evaluation of local recurrence. Follow-up was subjective and included client feedback.
Simpson et al. (2004) and Fulcher et al. (2006) investigated a 2cm lateral margin to remove MCTs. Both studies had a small sample size of 23 MCTs. Combined results showed 95 percent of MCTs (44/46) were completely excised. Two dogs in the study by Fulcher et al. (2006) had incomplete histological margins and one dog received revision surgery two weeks post-excision. No local recurrence was found at 351 and 379 days respectively.
Pratschke et al. (2013) excised MCTs using a lateral margin equal to the MCT’s widest diameter (with a maximum lateral margin of 4cm) and a well-defined deep fascial plane. Complete excision was achieved in 85 percent of cases (40/47). One local recurrence (of a completely excised grade III MCT) was observed after 429 days. The study had a small sample size, a relatively short follow-up period, adjuvant treatments and a death from gastric dilatation-volvulus one day post-surgery.
Itoh et al. (2021) used the proportional excision approach of Pratschke et al. (2013) for 24 MCTs. No local recurrence was found at a median follow-up of 990 days. The study only included small MCTs (2.6cm or less in diameter).
Chu et al. (2020) compared the completeness of excision using lateral margins of 2cm or less for tumours less than 2cm in diameter, and 3cm lateral margins (irrespective of diameter). They showed histologically tumour-free margins in 93 percent (43/46) and 92 percent (34/37) of the groups respectively. Local recurrence was not studied; however, a prospective clinical study with a two-year follow-up (Milovancev et al., 2019) has shown that narrow histological margins do not always correlate with local recurrence.
Saunders et al. (2020) used a proportional margin excision width based on the largest MCT lateral diameter up to 2cm; 2cm margins were used for MCTs with a diameter over 2cm. The local recurrence rate was 3 percent (3/100). Only high-grade tumours recurred. This study had the largest sample (100 MCTs).
No correlation could be established between conservative versus wide surgical excision and completeness of histological margins due to differences in histological margin classification methods and sampling methods. No significant association between tumour diameter and completeness of excision was shown. The clinical significance of a relationship between surgical margins and completeness of excision and the likelihood of metastatic spread could not be evaluated.
The clinical significance of a relationship between surgical margins and completeness of excision and the likelihood of metastatic spread could not be evaluated
There is increasing evidence that most grade I and II (low-grade) cutaneous MCTs can be excised using either 2cm lateral margins or the proportional margin approach without an increase in local recurrence rate. However, no clear recommendations can be made due to the low quality of the evidence. This evidence does not apply to grade III (high-grade) MCTs, which are biologically more aggressive, nor to subcutaneous MCTs, which lack a grading system and often have margins that are difficult to discern.
Further research in the form of multi-institutional studies with larger study populations would be beneficial.
The application of evidence into practice should take into account multiple factors, not limited to individual clinical expertise, patient’s circumstances, owner’s values, the individual case in front of you, the availability of therapies and resources, and the country, location or clinic where you work.
Knowledge Summaries are a resource to help reinforce or inform decision making. They do not override the responsibility or judgement of the practitioner to do what is best for the animal in their care.