๐ ็ธฝ็ฎ้ ๏ฝ ๐ ่ฑๆๅๆ๏ผๆฌ็ฏ๏ผ ๏ฝ ๐ ๅฎๆด็ฟป่ญฏ ๏ฝ โญ ็ฒพ่ฏ็ญ่จ
Melanoma
Melanoma
The routine use of Mohs micrographic surgery for invasive malignant melanoma remains controversial, and is often reserved for unique situations such as acral and facial melanomas where tissue preservation is essential for functional outcome.
However, in the setting of in situ disease, Mohs micrographic surgery for tumor extirpation has become increasingly accepted and utilized, with the aid of improved melanocytic immunohistochemical stains. Frozen sections must be cut thinner (in the order of 2 to 4 microns) in order to proficiently interpret melanoma in situ.
On routine hematoxylin and eosin staining, melanoma in situ demonstrates nested and confluent atypical melanocytes gathered along the dermal-epidermal junction. The lesions are often broad, especially in the case of lentigo maligna, in a background of solar elastosis. There may be pagetoid or โbuckshotโ-type spread of atypical melanocytes into the epidermis. The rete ridges are commonly effaced, and nonnested melanocytes often outnumber nested melanocytes. The nests, if there are any, vary in size and shape, and are often bizarre, elongated, or confluent. There is distinct asymmetry, and lateral borders are poorly defined. There may be a dense, lichenoid lymphocytic inflammatory infiltrate along the dermal edge of the lesion. Mitoses may be present, and there is often cytologic atypia.
In invasive malignant melanomas, poorly nested aggregates of atypical melanocytes extend beyond the dermalโepidermal junction into the dermis. The tumor is variably circumscribed with lateral asymmetry, and atypical melanocytes display a lack of normal maturation or dispersion with descent into the dermis. There is often prominent pagetoid or โbuckshotโ scatter into the epidermis. The rete ridges are commonly effaced, and non-nested melanocytes often outnumber nested melanocytes. Deep pigment may be present in melanocytic nests. The nests, if there are any, vary in size and shape, and are often bizarre, elongated, or confluent. There is often a lymphocytic inflammatory infiltrate at the base of the lesion, and plasma cells may be present as well. Mitoses, including deep mitoses, may be seen, and there is often cytologic atypia.
Historically, the utility of Mohs micrographic surgery for atypical melanocytic proliferations, including melanoma in situ, was limited given the poor diagnostic recognition of atypical melanocytes on frozen section. However, with the advancement of immunohistochemical stains and development of adequate staining techniques for frozen section tissue, the resolution and diagnostic accuracy for atypical melanocytic proliferations have advanced greatly.
Currently, the most commonly used immunohistochemical stain used for intraoperative assessment of melanoma margins during Mohs micrographic surgery is the MART1 (Melan-A) stain. Immunohistochemical staining for MART1 is helpful in detecting both benign and malignant melanocytic proliferations, and has become the immunohistochemical stain of choice for the detection of malignant melanoma in situ using Mohs micrographic surgery. However, it is important to note that the MART1 antibody stain is a highly sensitive cytoplasmic stain; there is often significant background staining of melanocytes in the setting of chronic sun-damaged skin, and thus using MART1 to differentiate between benign and malignant melanocytic proliferations for tumor margin assessment may prove challenging. Additionally, MART1 does not
stain desmoplastic melanomas. For a full discussion of Mohs surgery for melanoma in situ, see Chapter 31.