A 77-year-old man presented to the dermatologist's office with a lesion on the skin of his chest. There was no history of any skin malignancies. Clinical examination showed an irregularly contoured and irregularly pigmented dark brown lesion with variable colors of dark brown and black measuring 1.6 cm in its greatest dimension. The lesion was completely excised.

The pathology department received this as an elliptic skin excision specimen, 2.1 × 1.0 × 0.6 cm, with a pale tan hair-bearing skin surface. An eccentric dark brown elevated skin lesion 1.6 cm in its greatest dimension with irregular borders and a variegated surface was present. The deep margin consisted of tan-yellow subcutaneous tissue.

A histologic examination (Figure 1) showed atypical melanocytes forming confluent nests along the dermal-epidermal junction and infiltrating as groups and single cells through the overlying epidermis to the granular cell layer. These cells also infiltrated the papillary and reticular dermis as nests and sheets showing mitotic activity. The depth of invasion was 0.66 mm. No ulceration, regression, or vascular or neural invasion was identified. A nodule of a tumor 0.15 mm in transverse diameter was present in the deep reticular dermis (Figures 1 [arrow] and 2). This nodule was not contiguous with the bulk of the proliferation and was 0.96 mm from the granular cell layer of the epidermis. The lesion was completely excised.

What is your diagnosis?

The early vertical growth phase melanoma was first described by Clark et al.1 The early vertical growth phase can be distinguished from the radial growth phase in several ways,2 the most important criterion being the presence of a dominant nest within the papillary dermis that is conspicuously larger than any nest within the epidermis and that forms an expansile nodule. The cells comprising this nodule are cytomorphologically different from those of the intraepidermal component, and they invariably show conspicuous nucleolation, coarse chromatin, and irregularly thickened, notched nuclear chromatinic rims. Several such nodules or their coalescence indicates a progression to the fully evolved vertical growth phase melanoma. It has been shown that the presence of the vertical growth phase incurs a risk for metastasis, in contrast to the radial growth phase–confined lesions, for which surgical excision is almost always curative with the proviso that regression is not identified in the primary tumor.3,4 A radial growth phase is defined as a neoplastic proliferation of malignant melanocytes that grows either within the epidermis, the papillary dermis, or both in a manner that is oriented parallel to the epidermal surface.2 The presence of a radial growth phase in this tumor, although not illustrated in this study, precluded a diagnosis of nodular melanoma, in which, by definition, a radial growth phase is absent. The survival of patients with invasive melanoma in a vertical and/or radial growth phase can be predicted on the basis of evaluating several light microscopic parameters including measured depth, mitotic count, host response, sex, anatomic site, and presence or absence of regression, angioinvasion, ulceration, or, as in this patient, microscopic satellites.

Microscopic satellites are typically characterized by reticular dermal and/or subcuticular nodules of a tumor greater than 0.05 mm in diameter beneath the principal invasive tumor mass but separated from it by normal tissue.2 These satellites may or may not represent intradermal metastases. Melanomas with microsatellites are more likely to have regional lymph node metastases than are lesions of similar thickness without microsatellites.5,6 In revisions to the American Joint Committee on Cancer staging system for melanoma (2002), satellites were moved from the primary tumor category (ie, T4) to the N category (ie, N3); therefore, the presence of a microscopic satellite constitutes evidence of stage IV disease.2 It is critical to recognize microsatellites, as they are associated with a decreased incidence of disease-free survival as well as overall survival.7–9 

Clark
,
E. H. Jr
,
D. E.
Elder
,
D. I. V.
Guerry
,
M. N.
Epstein
,
M. H.
Greene
, and
M.
van Horn
.
A study of tumor progression: the precursor lesions of superficial spreading and nodular malignant melanoma.
Hum Pathol
1984
.
15
:
1147
1165
.
Crowson
,
A. N.
,
C. M.
Magro
, and
M. C. Jr
Mihm
.
Malignant melanoma.
In: Crowson AN, Magro CM, Mihm MC Jr. The Melanocytic Proliferations: A Comprehensive Textbook of Pigmented Lesions. New York, NY: John Wiley and Sons; 2001:281–397
.
Guerry
,
D. I. V.
,
M.
Synnestvedt
,
D. E.
Elder
, and
D.
Schultz
.
Lessons from tumor progression: the invasive radial growth phase of melanoma is common, incapable of metastasis and indolent.
J Invest Dermatol
1993
.
100
:
342
345S
.
Elder
,
D. E.
,
D. I. V.
Guerry
, and
M. N.
Epstein
.
et al
.
Invasive melanomas lacking competence for metastasis.
Am J Dermatopathol
1984
.
6
:(
suppl 1
).
55
61
.
Harrist
,
T. J.
,
D. S.
Rigel
, and
C. L. Jr
Day
.
et al
.
“Microscopic satellites” are more highly associated with regional lymph node metastases than is primary melanoma thickness.
Cancer
1984
.
53
:
2183
2187
.
Mraz-Gernhard
,
S.
,
R. W.
Sagebiel
,
M.
Kashani-Sabet
,
J. R. I. I. I.
Miller
, and
S. P.
Leong
.
Prediction of sentinel lymph node micrometastasis by histological features in primary cutaneous malignant melanoma.
Arch Dermatol
1998
.
134
:
983
987
.
Rao
,
U. N.
,
J.
Ibrahim
,
L. E.
Flaherty
,
J.
Richards
, and
J. M.
Kirkwood
.
Implications of microscopic satellites of the primary and extracapsular lymph node spread in patients with high-risk melanoma: pathologic corollary of Eastern Cooperative Oncology E 1690.
J Clin Oncol
2002
.
20
:
2053
2057
.
Day
,
C. L.
,
T. J.
Harrist
, and
F.
Gorstein
.
et al
.
Malignant melanoma: prognostic significance of “microscopic satellites” in the reticular dermis and subcutaneous fat.
Ann Surg
1981
.
194
:
108
112
.
Leon
,
P.
,
J. M.
Daly
,
M.
Synnestvedt
,
D. J.
Schultz
,
D. E.
Elder
, and
W. H. Jr
Clark
.
The prognostic implications of microscopic satellites in patients with clinical stage I melanoma.
Arch Surg
1991
.
126
:
1461
1468
.

Author notes

Corresponding author: A. Neil Crowson, MD, Regional Medical Laboratories, St John Medical Center, 1923 S Utica Ave, Tulsa OK 74104 ([email protected])