Histopathological reporting plays a critical role in guiding the surgical oncologist’s management plan in treatment of primary cutaneous melanoma. The International Collaboration on Cancer Reporting (ICCR) espouses various components of structured histopathological reporting as “essential” or “recommended.” From a surgical oncologist’s perspective, we discuss the clinical relevance of each essential component, as well as prognostic and treatment implications with regard to treatment planning.

New Zealand and Australia possess the highest incidence of melanoma in the world .In patients with newly diagnosed early-stage primary cutaneous melanoma, surgery remains the mainstay of initial treatment and is therefore usually orchestrated by the surgical oncologist. The surgical oncologist’s management plan depends on patient characteristics and histopathological features of the primary lesion following excisional biopsy. Therefore, the histopathological report plays a central role in guiding initial treatment, staging, and prognosis advice provided to melanoma patients.

The ICCR guidelines were established following evaluation of existing histopathological guidelines by the Royal College of Pathologists (United Kingdom) (RCPath), Royal College of Pathologists of Australasia (RCPA), and College of American Pathologists (CAP) [2]. Current “essential” (mandatory/standard) and “recommended” (nonmandatory/guideline) components of structured histopathological reporting for primary cutaneous melanoma.These components are important in evaluating prognosis, treatment options, candidacy for clinical trials, and standardized outcomes assessment. The preanalytical elements and components of macroscopic histopathological assessment are outside the scope of this article and are not discussed.

Primary lesion Breslow thickness bears the most significant prognostic and surgical implications and represents a cornerstone of American Joint Committee on Cancer (AJCC) staging.While substaging is further determined by lesion ulceration, Breslow thickness represents the fundamental determinant of T-staging .Furthermore, Breslow thickness acts as the basis of wide local excision (WLE) margins. Current guidelines recommend invasive melanomas < 2 mm in thickness to be excised with at least 1 cm margin, while melanomas ≥ 2.0 mm are excised with at least 2 cm margins.

Breslow thickness is also an independent predictor of sentinel lymph node (SLN) status .In a retrospective review of 221 patients undergoing sentinel node biopsy, there is SLN positive rate of 4.8% in T1 patients, 11.2% in T2 patients, 28.1% in T3 patients, and 46.5% in T4 patient.Further data supports performing sentinel node biopsy (SNB) for microscopic staging of the regional lymph node basin when tumour thickness meets or exceeds 1 mm, or greater than or equal to 0.75 mm with other high risk features such as ulceration and/or high mitotic activity .

After Breslow thickness, both mitotic rate and ulceration reporting are important for the surgical oncologist in treatment planning. Mitotic rate is no longer considered a staging criterion for T1 melanoma in the most recent AJCC guidelines .However, both features correlate with potential for metastatic spread and prognosis. Mitotic rate, as a sign of biologic activity, is particularly important in thin melanomas, where mitotic activity ≥ 1/mm² is associated with a decrease in 10-year survival from 95% to 88% .5-year survival rate in ulcerated melanomas is proportionately worse than no ulcerated melanomas of the same T stage, while being similar to nonulcerated melanomas of the next highest T stage.

In addition to low thickness, ulceration and mitotic rate can also influence the surgical decision to pathologically stage the regional lymph node basin with SNB. While SNB positivity has been reported at approximately 5% of all primary melanomas < 1 mm overall, the rate increases up to 20% for patients with thickness between 0.75 and 0.99 mm in the presence of mitotic rate ≥1/mm² and/or ulceration.This is important as melanomas ≤ 1 mm are reported to comprise over 70% of diagnoses made and also comprise 25% of all melanoma-specific deaths.

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Niloufer sobbrio

Associate Managing Editor