Desmoplastic Malignant Melanoma: A Systematic Review

M.B. Lens; J.A. Newton-Bishop; A.P. Boon

Disclosures

The British Journal of Dermatology. 2005;152(4):673-678. 

In This Article

Discussion

DM is an uncommon form of melanoma. Thus, it is important to understand its clinical characteristics and morphological patterns better as the experience of it in any one institution is low. There is a lack of statistically significant studies on the behaviour of DM due to the small number of patients included in the studies, patients' advanced age and short follow-up. Our study pooled the data from all published studies evaluating the characteristics of DM and thus represents the currently largest sample size.

DM is easily missed or misdiagnosed in the early stage, as it is often clinically innocuous and quite distinct from other types of melanoma.[4,24] We confirm in this study that DM usually has an advanced Breslow thickness at the time of presentation, which probably results from the difficulties in clinical diagnosis.

This analysis shows that patients diagnosed with DM are older (mean age around 63 years) than patients with unselected melanoma (the mean age for patients with superficial spreading melanoma is mid-40s). There is a male predilection, with a male/female ratio of almost 2 : 1.

The head and neck were the most common sites of DM for both sexes, although it can be also located on the trunk and upper limbs and in less expected sites such as the lower limbs, oral or genital mucosa. An increased association with lentigo maligna melanoma may support the possible link of DM with sun exposure.[25]

Histopathological diagnosis of DM is sometimes difficult and represents a significant challenge to the pathologist. The absence of pigmentation is probably the major cause of failure to recognize DM as melanoma histologically. Careful pathological examination with a critical review of multiple sections is required in order to avoid failure in the diagnosis of DM.[6,26] The use of immunohistochemistry (testing for S100 antigen) is suggested as a useful tool in establishing the diagnosis.

Close follow-up is necessary to detect recurrences and metastatic disease in all patients with melanoma including those with DM. Follow-up of patients with DM showed that DM is characterized by a high incidence of local recurrence, low incidence of lymph node metastases, and a propensity to develop systemic metastases. This is in contrast to other types of cutaneous melanoma where local recurrence is rare and the probability of lymph node metastases is mainly related to the thickness of the lesion.

Review of the published studies showed that local recurrence in DM is associated with an increased risk of developing additional local recurrences and an increased risk of developing systemic metastases. The high incidence of local recurrence after excision of the primary DM may be attributed to the clinical misdiagnosis of lesions, difficulty in the pathological examination and interpretation of specimens, inadequate surgical excision, high Breslow thickness of the tumour at time of diagnosis, and the neurotropic nature of infiltration.[10]

Our pooled analysis showed that the incidence of local recurrence among studies in which the mean Breslow thickness was < 4·0 mm was 19·5%, while among studies with the mean Breslow thickness > 4·0 mm the rate of local recurrence was 40·2%.

It was suggested that neurotropism is related to an increase in the frequency of local recurrences.[27] Also, it seems that neurotropism is associated with a significant decrease in survival in patients with DM.[27] However, we were unable to establish the association between neurotropism and local recurrence rate and survival due to the lack of the relevant raw data from the studies included in our analysis.

Although DMs are thicker lesions at the time of presentation compared with other variants of melanoma, the incidence of nodal metastasis is lower than in other forms of cutaneous melanoma where the incidence of regional metastasis as the site of first clinical relapse ranges from approximately 45% to 65% of all recurrences and correlates with the Breslow thickness of the primary tumour.[28] Our study demonstrated that lymph node involvement was present in 7·1% of the patients enrolled in included studies, showing no correlation with the Breslow thickness of the primary DM. The low incidence of lymph node metastasis in line with that seen in patients with soft tissue sarcoma suggests a different biology and natural history for DM compared with other types of melanoma. Indeed, DMs behave in a similar way to malignant schwannoma, from which it may also be difficult to make a histological distinction.

Systemic metastases appear to be related to previous recurrences and to depth of lesion. The lung is the most common site of systemic metastases. Some data suggest that DM may have an improved prognosis over the other forms of cutaneous melanoma. In other studies the survival from DM was not significantly different than from conventional melanoma. The aggressive clinical behaviour of DM seen in these studies can be attributed to the misdiagnosis of the early tumours and inadequate assessment of margins.

Prompt surgical excision of DM is the treatment of choice as it may decrease the chance of multiple local recurrences requiring multiple resections, or even evolution into metastatic disease. Although currently there is a trend towards narrower excision margins for cutaneous melanoma, optimal margins for DM are not established. Because of the unique microscopic and clinical behaviour of DM, routine recommendations for surgical resection of the more common melanomas may not apply to DM.[24] Many surgeons advise a minimum clearance margin of at least 1 cm. The problem with DM is that most DMs are invasive to a significant degree by the time of diagnosis, which makes it difficult to achieve clear surgical margins on an initial resection, especially if the tumour is present in an area in which large excisions are difficult functionally and cosmetically, such as on the face.

The low incidence of regional lymph node metastases in patients with DM suggests that elective lymph node dissection is not indicated in these patients. Recent studies advocate the use of sentinel lymph node biopsy (SLNB) and selective lymph node dissection as the most appropriate method for evaluation of the lymph node basins.[10] However, there is insufficient evidence on this matter and a multicentre study is needed to assess the clinical significance of SLNB in patients with DM.

The use of radiation therapy, adjunctive chemotherapy and immunotherapy has not been sufficiently studied in patients with DM. Some authors recommended adjuvant postoperative radiation therapy as a part of treatment of DM, claiming that it may be beneficial for local control as it can reduce the high rate of local recurrence of DM after surgical resection.[8,29] However, the number of patients with DM treated with one of these modalities is too small to establish a strong clinical judgement when considering postsurgical treatment of a patient with DM.

This review has highlighted the distinctive clinical behaviour and histological features of DM. Better knowledge of this type of melanoma should lead to its improved and more effective management.


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