Tumor Thickness and Modified Clark Level in Canine Cutaneous Melanocytic Tumors

Abstract

Breslow thickness and Clark level are prognostic factors for human cutaneous melanomas. Breslow thickness is measured with an ocular micrometer from the top of the granular layer of the epidermis to the deepest invasive cell across the broad base of the tumor, while Clark level is based on the anatomical level of invasion through the layers of the dermis. Because of the anatomical differences between humans and dogs, we evaluated the tumor thickness and a modified Clark level in 77 canine primary cutaneous melanocytic tumors. Tumor thickness (using both a traditional and a more convenient system) and modified Clark level were measured and associated with histological diagnosis and clinical outcome. Tumor thickness was a prognostic factor, being greater in animals with shorter overall survival and disease-free time. Cutoffs of 0.95 cm and 0.75 cm defined a higher hazard for an unfavorable outcome and to develop recurrence/metastasis, respectively. Because of an excellent agreement between the 2 methods, it was concluded that tumor thickness could be measured with a ruler when an ocular micrometer is not available. Modified Clark level was not found to be relevant for prognosis. However, we suggest that both tumor thickness and a modified Clark level can be valid additional parameters when histological diagnosis is uncertain. Further studies, including a wider sample population, would be worthwhile to confirm the prognostic significance of these 2 parameters.

Canine Melanomas as Models for Human Melanomas: Clinical, Histological, and Genetic Comparison

“…Usually, surgical resection is curative [32,33,34,87,89], although some pathological characteristics, such as a mitotic index ≥3 over ten fields (otf) the presence of ≥20 nuclear atypia, a Ki67 index >15%, ulceration, lymphatic invasion, and tumors extending beyond the dermis, have a negative influence on prognosis [33,35,37,90,91]. More recently, Silvestri et al showed that Breslow thickness is significantly associated with histological malignancy, clinical outcome, and presence of recurrence/metastasis [93].…”

“…Cutaneous melanoma has a relatively benign behavior in dogs. Recent studies, evaluating outcomes after surgical excision, showed that the MST was 1363 days and not reached with 77%–88% of dogs alive at 1 year and 54% alive at 2 years [36,39,40,93,94] (Figure 2). In the series of 87 dogs (Laver et al, 2018), 12% of dogs had lymph node metastases and 3.7% had pulmonary metastases at diagnosis.…”

Tumour‐infiltrating lymphocytes in canine melanocytic tumours: An investigation on the prognostic role of CD3+ and CD20+ lymphocytic populations

“…Samples in this study were partially included in a previous study on the usefulness of tumor thickness and modified Clark level for the evaluation of canine melanocytic tumors. 11 All samples were histologically evaluated for the parameters having the greater validity for prognostic use in canine melanocytic neoplasia, according to the current literature. 10,11…”

“…11 All samples were histologically evaluated for the parameters having the greater validity for prognostic use in canine melanocytic neoplasia, according to the current literature. 10,11…”

“…Recently, the usefulness of tumor thickness as a prognostic factor has been underlined in the canine species: in line to what observed in humans with Breslow thickness, thicker melanocytic tumors seems to have a worse prognosis. 11,12 However, compared to the human medicine, some factors remain to be investigated and there is still the need to find other helpful indicators to better define the prognosis of canine melanocytic tumors.…”