Clinical Characteristics and Preliminary Morphological Observation of 47 Cases of Primary Anorectal Malignant Melanomas

The clinical data and paraffin-embedded samples of 47 cases of primary anorectal malignant melanomas (ARMMs) detected from 2004 to 2017 were collected to investigate the clinicopathological characteristics. The ARMMs were grouped according to tumour size, appearance of melanin granules in the plasma of the tumour cell, linearly patterned programmed cell necrosis (LPPCN) in tumour tissue and lymph node metastasis. On the basis of size, these tumours were divided into two groups: group I (volume of tumour >20 cm, or minimal diameter >1 cm and volume of tumour <20 cm, but >10 cm) and group II (volume of tumour <20 cm and minimal diameter <1 cm). The number of polyploid giant cancer cells (PGCCs) detected and vasculogenic mimicry (VM) observed were compared across the different groups. Immunohistochemical double-staining was used to confirm the differentiation of melanoma cells into fibroblasts and endothelial cells. The results of our study showed that PGCCs and VMs exist in ARMMs. The number of PGCCs was significantly higher in group I than in group II, in tumours with LPPCN than in tumours without LPPCN and in tumours with lymph node metastasis than in tumours without metastasis. VM channel formation was significantly higher in amelanotic ARMMs than in melanotic ARMMS. Furthermore, PGCCs and their generated erythroid cells can form VMs to supply the oxygen and nutrition to the tumour. Some tumour cells were positive for both, fibronectin or CD34, and HMB45. These results showed that the number of PGCCs and VMs were related to the development and progression of ARMMs.