Confocal microscopy prior to slow Moh’s surgery for lentigo maligna
Research type
Research Study
Full title
Reflectance confocal microscopy as a diagnostic adjunct in the evaluation of lentigo maligna margins prior to slow Mohs surgery - a review of data and cost analysis from a tertiary referral centre
IRAS ID
247222
Contact name
Marc Moncrieff
Contact email
Sponsor organisation
Norfolk & Norwich University Hospitals NHS Foundation Trust
Duration of Study in the UK
0 years, 3 months, 0 days
Research summary
Research Summary
Lentigo maligna (LM) is a subtype of pre-invasive melanoma associated with chronic sun exposure. It can develop into invasive melanoma called lentigo maligna melanoma (LMM). It typically has ill-defined margins so is challenging to remove surgically. The ideal treatment is surgical excision. A widely used method is slow Mohs’ surgery. In this, the visible portion of the tumour is removed with a margin, one layer at a time. The tissue that is removed is reviewed histologically but the results are not available until several days later. The patient will need return to hospital for further surgery if the tissue removed is not clear of cancer cells at the margins. This is repeated until the tumour is completely removed and despite the best efforts of surgeons, it can take multiple excisions. \n\nThere are increasing reports in the scientific literature that reflectance confocal microscopy (RCM) is useful in pre-surgical tumour margin mapping. RCM is a non-invasive imaging technique. This guides the surgeon on how much tissue to remove. Researchers propose that if the surgeon is able to more accurately remove the correct amount of tissue with the aid of RCM mapping, this will reduce the number of surgical excisions a patient may need. \n\nThis retrospective study will extract data from medical records of adult patients with LM or LMM who had slow Mohs surgery at Norfolk and Norwich University Hospitals NHS Foundation Trust between 2013 and 2018. A proportion of these patients had pre-surgical tumour mapping with RCM. We will compare outcomes of patients that had pre-surgical mapping versus those that did not. \n\nOur hypothesis is that pre-surgical mapping with reflectance confocal microscopy will be associated with reduction in number of surgical excision (mohs layers) required. Hence, it will be associated with reduction in surgical time, cost and improvement in patient experience.
Summary of Results
Lentigo maligna (LM) is a subtype of in situ melanoma that occurs on sun damaged sites, most often the head and neck. LM margins are often difficult to assess and standard excision with a 5mm margin has recurrence rates of 8-20%1. Complete circumferential and peripheral margin assessment with a staged excision, known as slow Mohs micrographic surgery (sMMS), is a method for optimising margin control but multiple layers may be required for tumour clearance. Reflectance confocal microscopy (RCM) has been used for diagnosis2 and margin mapping of LM with promising results3-6 although data is limited.
This objective of this study was to determine whether RCM margin mapping in LM cases is associated with differences in patient outcomes (including number of Mohs layers required and time to definitive repair of the resulting defect) compared with visual inspection with dermoscopy alone.
This single-centre retrospective cohort study was performed at the department of dermatology at Norfolk and Norwich University Hospital (NNUH), Norwich, United Kingdom. HRA approval was sought and given for this study (REC 18/YH/0484). All patients with head and neck biopsy-proven primary LM treated with sMMS between 2013 to 2018 were included.
All patients were discussed at a specialist skin cancer multidisciplinary team meeting where patients were selected for RCM mapping pre-surgery. For the RCM group, surgical margins were identified by RCM before surgery, marked by a surgical pen. LM was defined as the presence of three or more large atypical bright round or dendritic cells in the epidermis and/or at the dermo-epidermal junction on RCM. All of the tumours were removed by sMMS by experienced members of the NNUH Mohs team. The patient, tumour and MMS characteristics were extracted from electronic records.
The primary outcome measure was the number of Mohs layers required for tumour clearance. Additional outcomes included time to reconstruction and type of reconstruction. Categorical variables were analysed using Fisher’s exact test and continuous variables were compared using Mann-Whitney U test, in addition to standard descriptive statistics.
In total, 47 patients with head and neck biopsy-proven primary LM had excision with sMMS between December 2013 – December 2018. Twenty-one (44.6%) patients had RCM mapping (mean age 67.9 ± 12.5 years; 10 men and 11 women) and 26 (55.4%) patients (mean age 67 ± 11.0 years; 10 men and 16 women) had clinical and dermoscopic examination only.
The tumour was cleared with one layer in 81% of cases with RCM mapping compared to 61.5% using visual inspection mapping. The mean number of layers required for tumour clearance in RCM mapped patients was 1.29 ± 0.64; compared with 1.54 ± 0.81. This was not statistically significant. However, RCM mapping did significantly reduce time-to-repair (mean 14 days mapped vs 27 non-mapped; median 4 vs 7 days; t-test p=0.038). There were no significant differences in reconstruction methods between the two groups.
Our findings are in keeping with previously published evidence that the pre-operative use of RCM to map the border of lesions5, 6 may improve initial complete excision rates. An additional benefit of using RCM to map LM is that both patient and clinician are better informed as to the extent of surgery required. This allows planning of reconstructive options prior to surgery, with appropriate involvement of other surgical teams to achieve optimal outcomes. This is combined with the benefit that the surgery itself may involve fewer layers, with a reduced risk of incomplete excision.
Limitations of our study include the small sample size, retrospective design (meaning some data was unavailable such as presurgical lesion size) and the lack of patient-reported outcomes. A potential bias lies in the non-randomised selection of patients which could have resulted in a tendency to select more ill-defined tumours for RCM mapping. RCM is operator dependent and has a significant learning curve before reliable results can be obtained. Therefore, it is uncertain if our results can be generalised to other dermatology services. We acknowledge that RCM can be more time-consuming than dermoscopic examination and in the immediate future will be limited by lack of equipment and operators. However, as RCM is more widely used, this useful addition to clinical practice will allow improved diagnostic accuracy of LM2 and surgical planning.
In conclusion, this study shows that RCM mapping was associated with a significant reduction in the time to repair for surgical wound after LM excision, compared with those not receiving RCM mapping. We did not show a statistically significant difference in number of Mohs layers required when using RCM mapping. Future studies with randomisation and a larger cohort may yield clearer result.
REC name
Yorkshire & The Humber - Bradford Leeds Research Ethics Committee
REC reference
18/YH/0484
Date of REC Opinion
4 Dec 2018
REC opinion
Favourable Opinion