索突性黑素瘤（DM）是一种罕见的黑色素瘤亚型，具有独特的临床病理特征。当索突性黑素瘤的比例≥90%时，它被分为纯粹的索突性黑素瘤（PDM），当其比例<90%时则为混合型索突性黑素瘤（MDM）。研究报道了PDM相对于MDM和非DM患者存在着更低的哨兵淋巴结活检（SLNB）阳性率。因此，有些人建议PDM患者不要进行SLNB。但在部分黑素瘤的局部活检中发现PDM时，存在抽样偏差可能会低估MDM的情况，但据我们的了解，此前尚未对此进行评估或量化。本研究的目的是，评估皮肤黑素瘤患者初始部分活检中的PDM比例与完全切除后整个肿瘤的比例之间的一致性。次要目的是确定患者因此未进行SLNB的频率。我们从澳大利亚黑素瘤研究所（MIA）数据库中选取了78例皮肤黑素瘤和从纪念斯隆·凯特林癌症中心（MSKCC）中选取了23例初步活检包含PDM和随后广泛切除的残留浸润性黑色素瘤。分析了所有患者的临床病理特征，包括是否进行SLNB，SLNB的结果以及任何随后的复发。在完全切除病灶中，90%的病例（91/101）仍被归类为PDM，10%的病例（10/101）被重新分类为MDM，这是终末索突性黑素瘤亚型分类的显著变化（p<0.001）。索突性黑素瘤的比例在初始活组织活检与切除活检之间也有显著差异（p=0.004）。48例患者进行了SLNB，其中有2例（4.5%）转移性黑素瘤阳性，两例为PDM，其中10例在切除标本中显示为MDM。这10例中的4例接受了SLNB，结果为阴性。随访期间有22位患者出现复发（中位随访时间30个月，范围1-192个月），其中3位切除标本为MDM。有1位患者没有进行SLNB，出现区域性淋巴结复发。在这项研究中，发现初步活检中的PDM的百分比有10%的风险不能代表整个病灶，导致在切除标本中被重新分类为MDM。如果在这些情况下没有进行SLNB，则可能会错过阳性SLNB（我们的研究中有1例患者），这可能会影响患者的治疗选择。我们建议在初步活检中发现PDM时，在诊断相对于整个病变较小的情况下应慎重考虑不进行SLNB。如果在这些情况下没有在广泛切除时进行SLNB，则应通过淋巴显影图来绘制SLNs，以便进行仔细的随访，使更早地检测和治疗淋巴结疾病成为可能。版权所有©2023年澳大利亚病理学学会。保留所有权利。

Desmoplastic melanoma (DM) is an uncommon subtype of melanoma with distinct clinicopathological features. It is classified into pure desmoplastic melanoma (PDM) when the proportion of desmoplastic melanoma is ≥90% of the dermally-invasive component, and mixed desmoplastic melanoma (MDM) when the proportion of desmoplastic melanoma is <90%. Studies have reported a lower sentinel lymph node biopsy (SLNB)-positivity rate in PDM compared to MDM and non-DM. As a result, some have recommended not performing SLNB in PDM patients. When PDM is identified in a partial biopsy of a melanoma, there is a risk that sampling bias may under-recognise MDM, but to the best of our knowledge this has not been previously assessed or quantified. The aim of this study was to assess the concordance of the proportion of desmoplastic melanoma in an initial partial biopsy of PDM with the proportion in the entire tumour following complete excision, in patients with cutaneous melanoma. A secondary aim was to determine how frequently this potentially resulted in a patient not receiving a SLNB. Seventy-eight cases of cutaneous melanoma were identified from the Melanoma Institute Australia (MIA) database and 23 cases from the Memorial Sloan Kettering Cancer Centre (MSKCC), where an initial biopsy contained PDM and a subsequent wide excision had residual invasive melanoma. Clinicopathological features were analysed in all patients, including whether a SLNB was performed, the results of SLNB, and any subsequent recurrence. Ninety percent (91/101) of cases were still classified as PDM in the complete wide excision specimen while 10% (10/101) of cases were reclassified as MDM, which was a significant change in classification of final desmoplastic melanoma subtype (p<0.001). The proportion of desmoplastic melanoma was also significantly different between the initial and excisional biopsies (p=0.004). Forty-eight (48/101) patients had a SLNB, of which two (4.5%) were positive for metastatic melanoma; both cases were PDM in the excision specimen. Of the 10 cases demonstrating MDM in the excision specimen, the initial biopsy was a punch biopsy in six cases, shave biopsy in two cases and subcutaneous tissue was sampled in two patients (one punch biopsy, one incisional biopsy). Four of these 10 patients underwent SLNB which was negative in all cases. Twenty-two patients developed recurrence in the follow-up period (median 30 months, range 1-192 months), three with MDM in their excision specimen. One patient did not have a SLNB and developed regional lymph node recurrence. In this study there was a 10% risk that the percentage of desmoplastic melanoma in an initial biopsy of PDM was not representative of the entire lesion, resulting in reclassification as MDM in the excision specimen. If a SLNB is not performed in such cases, a positive SLNB may be missed (one patient in our study) which could impact treatment options for the patient. We recommend caution in not offering a SLNB in the setting of an initial biopsy of PDM if the biopsy is small compared with the overall lesion. If a SLNB is not procured at the time of wide excision in such cases, the SLNs should still be mapped by lymphoscintigraphy to facilitate careful follow up and to enable earlier detection and treatment of nodal disease.Copyright © 2023 Royal College of Pathologists of Australasia. All rights reserved.