Malignant transformation in a cellular blue nevus of long duration

ARTICLE

A 77-year-old female patient was admitted to the dermatology clinic of another hospital with a lesion on her left buttock, which had been present for 60 years (Fig. 1). She noticed itching and bleeding of the lesion during the last six months. A punch biopsy was performed. Dermatological examination revealed a 1.6 x 1.1 cm greyish-blue firm plaque with well-defined borders, located on the lateral side of left buttock. There was no regional nodal involvement. Epiluminescence microscopy was suggestive of a dermal melanocytic proliferation. Typical topographic location, clinical and dermatoscopic examination data suggested a blue nevus.

According to the biopsy interpretation a primary surgical treatment was planned. A wide elliptical excision, intraoperative lymphatic mapping with patent blue-V and radionuclide4 (Tc-99) and sentinel lymph node biopsy were performed. Lymphoscintigraphic examination showed increased radionuclide uptake in 4 lymph nodes of the inguinal area. These nodes were excised.

Gross sections (Fig. 2) showed a deep seated pigmented tumor extending from the superficial dermis to the subcutaneous fat. The color was grey-black. The margins were bulging at the superficial portion and somewhat blurred at the deeper part.

Histopathological examination showed a pigmented lesion composed of fascicles and whorls of spindle shaped cells with light staining cytoplasm, a few heavily pigmented dendritic melanocytes and clusters of melanophages extending to the deep subcutis (Fig. 3). Beneath the epidermis and in the deep reticular dermis an area with pleomorphic spindle and epiteloid cells with readily apparent nuclear hyperchromasia, giant cells and a few mitoses were noted (Fig. 4). The tumor had deep infiltrative margins and a ragged deep border. Architectural atypia was marked with irregular placement of deep dermis nests and irregular pigment distribution. Atypical mitoses and necrosis were not noted.

Evaluation of proliferative activity using Ki-67 (MIB-1) antibody showed a nuclear labelling index reaching 10% in the foci composed of pleomorphic cells.

Malignant transformation in a cellular blue nevus of long duration

The diagnosis of malignant blue nevus (MBN) was based on the reported recent changes in a quiescent lesion, the unequivocally observed cellular blue nevus (CBN), background and histopathological features highly suggestive of the malignancy.

Histopathological examination showed that the excised lymph nodes were free of metastasis. Complete clinical and radiological evaluation (including chest X-ray, abdomen scan and total body computed tomography scan) failed to reveal other neoplastic deposits. The patient is alive and well after a follow-up of 11 months.

Comments

Malignant blue nevus (MBN) is a rare neoplasm usually documented on a previously existing blue nevus [1-4] and most reports consist of isolated cases and small series. The largest reported serial is that of Connelly and Smith's [3] and is based on data about 12 cases. These authors have reviewed the English literature and found 21 additional cases [3]. Strictly defined, the diagnosis of MBN requires the presence of a malignant melanocytic lesion and a clearly recognisable background, which is most often a CBN.

Criteria for malignancy in such lesions are not unanimously accepted. Those proposed by Conelly and Smith [3] are the presence of a background of blue nevus, mostly of the cellular type, a distinct appearing malignant component defined by the presence of atypical mitoses and necrosis. Yet these were not present in any of the 12 cases presented by the same authors. We think the lack of consistency in application of these criteria by different authors have led to the emergence of a new category, the atypical cellular blue nevus (ACBN) [4-6].

"Atypical cellular blue nevus" (ACBN) is a histopathological designation which characterizes a lesion with worrisome morphological features like greater size, increased cellularity, deep infiltrative margins, a lymphocytic host response, cellular pleomorphism, increased mitotic activity and areas of necrosis [5, 7], but which still does not fulfil the criteria for overt MBN.

Histopathological differential diagnosis between MBN, ACBN and BN-like metastatic melanoma [8] is difficult. Insufficient sampling leading to non-recognition of the CBN background can result in a diagnostic error.

As a potential objective means of separating CBN, ACBN and MBN, evaluation of the proliferative activity has recently received attention. Pich, et al. [9] reported that nucleolar organiser regions (AgNORs) and proliferating cell nuclear antigen (PCNA) staining could allow differentiation between MBN and CBN. However a recent study by Tran, et al. [5] used PCNA, Ki-67 (MIB-1) immunostaining to compare CBN and ACBN, and no significant difference was found, although the staining level was higher for ACBN.

MBN has definite metastatic potential and should therefore be removed by wide surgical excision. Incomplete excision may result in local recurrence [10]. Since the tumor usually metastasizes to regional lymph nodes, a clinical and scintigraphic evaluation and sentinel node biopsy are mandatory. In our patient, although 4 lymph nodes were suspicious by scintigraphic evaluation, no involvement has been detected in histopathological examination and the patient is free of disease after 16 months of follow-up.

In conlusion, it is worthy saying that malignant transformation of cellular blue nevus is a rare phenomenon and the histopathological criteria formulated to differentiate between CBN, ACBN and MBN are still not clearly defined. Furthermore, follow-up information of these patients will surely help to define more reliable criteria.

* This case was presented at XXIst. National Congress of Plastic and Reconstructive Surgery, 30 September-3 October 1999, Kusadas´y, Turkey.

References

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