[517] Lentiginous Compound Dysplastic Nevus of the Back – A Mimic of Recurrent Nevus and Malignant Melanoma with Regression

Katy Linskey, Adriano Piris, Martin C Mihm, Mai Hoang. Massachusetts General Hospital, Boston, MA; Brigham & Women's Hospital, Boston, MA

Background: Melanocytic nevi of the back can have 'recurrent' features attributed to repeated trauma; however, these features have not been emphasized in the literature.
Design: Retrospective review of 1,015 consecutive lentiginous compound dysplastic nevi (LCDN) from a back location without prior biopsy between 1/2010-2/2011 yielded 54 cases with localized fibrosis. For histologic comparison, 58 consecutive cases of melanoma with regression diagnosed between 6/2004-8/2011 were included.
Results: The median age of LCDN patients was 43 (range 21-85). 27/54 (50%) and 27/54 (50%) LCDN cases with fibrosis had a “recurrent” and traumatic pattern, respectively. The median age of regressed melanoma patients was 63 (range 24-93) and median Breslow depth was 0.61 mm (range 0.2-49). Junctional extension beyond the dermal fibrosis, adnexal involvement, effacement of the retiform epidermis, cytologic atypia, nests of melanocytes admixed with lymphoid infiltrate, elastosis below dermal fibrosis, prominent melanophages, and plasma cells were significantly more frequent in melanoma.

Table 1: Summary of histologic features.
 Regressing melanomaLCDNP value
Lentiginous junctional melanocytic proliferation58/58 (100%)50/54 (93%)0.051
Confluent growth pattern52/58 (90%)22/54 (41%)<0.0001*
Extension beyond dermal scar/fibrosis58/58 (100%)0/54 (0%)<0.0001*
Adnexal involvement50/58 (86%)14/54 (26%)<0.0001*
Effacement of the retiform epidermis49/58 (84%)28/54 (52%)0.0002*
Pagetoid spread52/58 (90%)11/54 (20%)0.0001*
Junctional mitotic figures4/58 (7%)1/54 (2%)0.365
Cytologic atypia (prominent nucleoli, enlarged nucleus & cell size)51/58 (88%)15/54 (28%)<0.0001*
Prominent cytoplasmic melanin pigment25/58 (43%)12/54 (22%)0.026*
Nests of melanocytes admixed with lymphoid infiltrate25/58 (43%)2/54 (4%)<0.0001*
Elastosis below dermal scar/fibrosis11/58 (19%)0/54 (0%)0.0006*
Dermal nevus below dermal scar/fibrosis2/58 (3%)49/54 (91%)<0.0001*
Dermal inflammation#40/58 (69%)14/54 (26%)<0.0001*
Plasma cells#30/58 (52%)2/54 (4%)<0.0001*
Melanophages#30/58 (52%)2/54 (4%)<0.0001*
* Statistically significant, two-tailed P-value <0.05, Fisher's Exact test; #Scored as focal/subtle or marked; remaining features scored as present or absent

A dermal nevus component below the dermal fibrosis was significantly more frequent in LCDN.
Conclusions: LCDN of back can have 'recurrent' features despite lack of prior biopsy. Recognition of these histologic features can be helpful in distinguishing it from severely atypical melanocytic proliferation and melanoma with regression.
Category: Dermatopathology

Monday, March 19, 2012 8:15 AM

Platform Session: Section F, Monday Morning


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