Linear Malignant Melanoma In Situ: Reports and Review of Cutaneous Malignancies Presenting as Linear Skin Cancer

Abstract

Melanomas usually present as oval lesions in which the borders may be irregular. Other morphological features of melanoma include clinical asymmetry, variable color, diameter greater than 6 mm and evolving lesions. Two males whose melanoma in situ presented as linear skin lesions are described and cutaneous malignancies that may appear linear in morphology are summarized in this report. A medical literature search engine, PubMed, was used to search the following terms: cancer, cutaneous, in situ, linear, malignant, malignant melanoma, melanoma in situ, neoplasm, and skin. The 25 papers that were generated by the search and their references, were reviewed; 10 papers were selected for inclusion. The cancer of the skin typically presents as round lesions. However, basal cell carcinoma and squamous cell carcinoma may arise from primary skin conditions or benign skin neoplasms such as linear epidermal nevus and linear porokeratosis. In addition, linear tumors such as basal cell carcinoma can occur. The development of linear cutaneous neoplasms may occur secondary to skin tension line or embryonal growth patterns (as reflected by the lines of Langer and lines of Blaschko) or exogenous factors such as prior radiation therapy. Cutaneous neoplasms and specifically melanoma in situ can be added to the list of linear skin lesions.

Keywords: cancer; cutaneous; in situ; linear; malignant; malignant melanoma; melanoma in situ; neoplasm; skin.

Figure 1. Distant (left) and closer (upper right and lower right) views of the clinical presentation of the linear melanoma in situ on the left chest of a 72-year-old male.

The linear tumor (solid arrow) is horizontally positioned above the breast. The lateral sides are hyperpigmented and there is a small area of hypopigmentation in the center of the tumor. The melanoma in situ measures 8 x 2 mm with a resultant length-to-width ratio of 4:1.

Figure 2. Low (upper left), intermediate (upper right), and higher (lower left and lower right) magnification views of the pathology of the linear melanoma in situ from the left chest of a 72-year-old male.

There are compact orthokeratosis and focal parakeratosis; the epithelium (solid rectangle) is thinned. There is the elongation of the rete ridges (solid stars) and anastomosis of the tips of the rete ridges. Melanocyte nests (solid arrows) of variable size and shape are present in the lower layers of the epidermis. Lymphocytes and melanophages are present around the vessels in the papillary dermis (open circles). There is no invasion of the tumor melanocytes into the dermis (hematoxylin and eosin (HE) stain; upper left, x 4, upper right, x 10; lower left, x 20 and lower right, x 20).

Figure 3. Distant (top) and closer (lower right and lower left) views of the clinical presentation of linear melanoma in situ arising in a compound melanocytic nevus on the left mid-back of a 31-year-old male.

In addition to the tumor (solid arrow), numerous lentigos, appearing as brown patches also present on the upper back. The tumor is brown with overlying irregular black pigmentation. The tumor (solid arrow) measures 10 x 2.8 mm with a resultant length-to-width ratio of 3.6:1.