Anatomic Pathology / LICHENOID TISSUE REACTION IN MALIGNANT MELANOMA

Lichenoid tissue reactions can occur in malignant melanoma and may cause partial regression of the lesion. We studied a series of melanomas to determine how frequently lichenoid tissue reaction obscures the diagnosis of malignant melanoma. We retrospectively reviewed 342 cases of invasive malignant melanoma and melanoma in situ from the head, neck, chest, and back. Of the 342 cases, 23 (6.7%) had a lichenoid tissue reaction obscuring a portion of the lesion. In 6 cases (1.8%), the lichenoid tissue reaction replaced a major portion of the lesion. Knowledge of this phenomenon can prevent misdiagnosis. Lichenoid tissue reaction can obscure junctional melanocytes, making the diagnosis of malignant melanoma (MM) more difficult. Especially in the setting of clinically amelanotic lesions, this creates a potential for misdiagnosis of invasive or in situ malignant melanoma as benign lichenoid keratosis (BLK). We attempted to determine how frequently lichenoid interface dermatitis obscures the diagnosis of MM or melanoma in situ (MMIS). Materials and Methods A total of 342 cases of MM and MMIS were retrieved from the surgical pathology files of Wilford Hall Medical Center and Brooke Army Medical Center, San Antonio, TX, for the period January 1993 to June 2000. We reviewed 200 cases from the head and neck and 142 cases from the chest and back to determine whether a lichenoid tissue reaction obscured portions of the melanoma. The percentage of each lesion obscured by the lichenoid reaction was assessed. Lichenoid tissue reaction was defined as a band-like infiltrate of lymphocytes in the dermis that obscured the dermal-epidermal junction accompanied by necrotic keratinocytes (Civatte bodies) at the dermal-epidermal junction ❚Image 1❚. The reaction was considered to obscure the melanoma when no melanocytes could be identified in the H&E-stained sections in the area of the infiltrate. Standard H&E-stained slides were reviewed, as were all immunohistochemical stains ordered at the time the case was originally signed out. The clinical history of each lesion was reviewed subsequently. Ten BLKs and 10 MMs were selected randomly as control cases and stained with MART-1. Anatomic Pathology / ORIGINAL ARTICLE Am J Clin Pathol 2002;117:766-770 767 © American Society for Clinical Pathology Results A total of 23 cases (6.7%) were found to have a lichenoid tissue reaction obscuring at least a portion of the lesion ❚Table 1❚. The Table indicates the percentage of the specimen involved by melanoma and by lichenoid dermatitis. Lichenoid tissue reaction was demonstrated in 11 (5.5%) of 200 cases from the head and neck and 12 (8.5%) of 142 cases from the chest and back. Six cases (1.8%) demonstrated a large percentage of the lesion (30% or more) obscured by a lichenoid tissue reaction. Three (13%) of the lesions with a lichenoid tissue reaction were clinically amelanotic (cases 1, 2, and 3). All 3 lesions demonstrated areas of in situ melanoma in at least a portion of the specimen with H&E or MART-1 immunostaining. In case 1, the clinical differential diagnosis included basal cell carcinoma, squamous cell carcinoma, and actinic A B ❚Image 1❚ A, Biopsy specimen of malignant melanoma in situ demonstrating a lichenoid tissue reaction with the lymphocytic infiltrate obscuring the dermal-epidermal junction (H&E, ×40). B, Higher power of lichenoid infiltrate. Note the absence of melanocytes (H&E, ×100). ❚Table 1❚ Cases of Lichenoid Tissue Reaction in Malignant Melanoma and In Situ Lesions Percentage Percentage Percentage Case No. Clinical Impression Diagnosis Size Lichenoid Melanoma Normal 1 Nonpigmented MMIS 5 mm 30 50 20 2 Nonpigmented MMIS 5 cm 5 95 0 3 Nonpigmented MMIS 4 cm 5 95 0 4 Pigmented MM 12 mm 40 60 0 5 Pigmented MM 2 cm 2 75 23 6 Pigmented MMIS 2 cm 10 50 40 7 Pigmented MM 7 mm 2 80 18 8 Pigmented MM 8 mm 10 50 40 9 Pigmented MMIS 6 mm 10 75 15 10 Pigmented MMIS 2 cm 30 30 40 11 Pigmented MMIS 2 cm 50 20 30 12 Pigmented MM 13 mm 90 5 5 13 Pigmented MM 6 mm 2 90 8 14 Pigmented MMIS 2 cm 50 50 0 15 Pigmented MM >3 cm 5 95 0 16 Pigmented MM 5 cm 5 95 0 17 Pigmented MMIS 4 cm 10 90 0 18 Pigmented MMIS 10 mm 5 95 0 19 Pigmented MM 6 cm 2 98 0 20 Pigmented MMIS 3 cm 2 98 0 21 Pigmented MMIS >3 cm 20 80 0 22 No history MMIS 3 cm 10 30 60 23 No history MMIS >3 cm 1 99 0 MM, malignant melanoma; MMIS, malignant melanoma in situ. Dalton et al / LICHENOID TISSUE REACTION IN MALIGNANT MELANOMA 768 Am J Clin Pathol 2002;117:766-770 © American Society for Clinical Pathology keratosis. In cases 2 and 3, the clinical differential diagnosis included actinic keratosis and Bowen disease. In cases 1 and 2, the diagnosis was established with the help of MART-1 immunohistochemical staining. In 2 of the 23 lesions (cases 22 and 23), no history was provided. One of the 10 BLK control cases stained with MART-1 demonstrated short runs of confluent melanocytes and several enlarged multinucleated melanocytes adjacent to the lichenoid tissue reaction that were not present on the original H&E-stained section. Deeper sections revealed melanocytic nests confirmed by MART-1 immunostains (see the “Discussion” section).