| Naevoid melanoma
is a rare form of nodular melanoma that may mimic benign melanocytic lesions.
The lesions are called 'naevoid'
because the cytological and architectural features resemble features of
benign intradermal or compound melanocytic naevi.
Recent studies have shown that there is a significant local recurrence
and mortality rate in patients diagnosed with naevoid melanoma.
Histological features :
To make a diagnosis of naevoid melanoma a high index of suspicion
is essential.
An intraepidermal component is recognized at low power.
The intradermal component is composed of tightly packed nests of small
dark stained cells resembling naevus cells .
The cells display hyperchromatic mildly pleomorphic nuclei , scanty
cytoplasm and occasional prominent nucleoli.
Dermal mitosis may or may not be present.
A reactive stromal response is evident characterized by proliferation of
blood vessels and patchy lymphocytic infiltrate.
Immunohistochemistry: S100 protein & HMB45 are usually positive
The cells also express proliferating cell nuclear antigen (PCNA) and
Ki67 (using MIB-1) .
HMB45 may be negative in some cases.
Note: In Spitz naevus there is
stratification of staining . In the base of the lesion cellular staining
is less intense.
[Some clues to diagnosis of Nevoid melanoma: Hypercellularity ; Loss of
orderly arrangement of nests ; Cells present in strands and cords in
some cases; Presence of deep dermal mitosis ; Lack of maturation with
depth; Infiltrative pattern at the base of the lesion ]
Visit
Dr Weem's page- CLICK HERE
Case
link & discussion- (Dr Reed&Mihm)-CLICK
HERE
ARTICLE LINK
(full text):
CLICK HERE
| Similarities and
differences between Nevoid melanoma and compound naevus:
Nevoid malignant
melanoma small cell type:
Similarities: i) Cells are usually small ; ii) Pagetoid cells are
rare ; iii) Melanocytes are nested iv) Cells may disperse at the
base.
Differences:
Compound Naevus: Mitosis
is absent; Nucleoli inconspicuous at base of the lesion;
Nuclei not hyperchromatic ; HMB45 negative at base; MIB1 negative at
base.
Naevoid malignant melanoma (small cell type):
Mitosis present in
dermis ; Nucleoli visible at the base; Nuclei hyperchromatic ;
HMB45- positive at base; MIB-1 positive at base. |
| Similarities and
differences between Nevoid melanoma and Spitz's naevus:
Nevoid malignant melanoma large
cell type:
Similarities:
i) Cells tend to be large; ii) Pagetoid cells
may be present; iii) Melanocytes are nested iv)
Cells may disperse at
the base.
Differences:
Spitz's naevus :
Mitoses present in dermis, but rarely at the
base; cell size small at the base; Kamino bodies are common;
HMB-45 patchy positivity, may be at base; MIB-1 diminishes at base.
Naevoid malignant
melanoma (large cell type):
Mitoses present in
dermis even at base; Cell size large at base; Few Kamino bodies;
HMB-45 positive at base; MIB-1 undiminished at base. |
Verrucous Naevoid
Melanoma
Melanoma is characterized by
epidermal hyperplasia , elongation of rete ridges and overlying
hyperkeratosis. Clinically these lesions may be mistaken for seborrheic
keratosis.
(At low power some these lesions may resemble papillomatous benign
intradermal naevi.)
The tumour consists of small naevus like cells with no evidence of
maturation with depth. The lesion may demonstrate atypical junctional
component, asymmetric lateral growth pattern and area of regression.
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CASE LINK:
CLICK HERE
Verrucous
naevoid and keratotic malignant melanoma: a clinico-pathological study
of 20 cases. Histopathology 1993;23: 453-458
Verrucous-keratotic variations of
malignant melanoma. A clinicopathological study. Am J. Dermatopathol
1982; 4: 403-10
Verrucous pseudonaevoid melanoma. J Surg Oncol
1987;36: 134-7
|
Dr. Sampurna Roy MD
