The immunohistochemical expression of cell cycle proteins p16, cyclin D1, and pRb was assessed in 112 benign and malignant melanocytic tumors and correlated with tumor progression, prognosis, and outcome. Comparing benign and malignant tumors, there were significant differences in the median score for all 3 proteins, with decreased p16 (P = .000001), increased cyclin D1 (P = .01), and increased pRb in melanomas (P = .01). There was a progressive loss of expression of p16 with progression from benign naevi to primary melanomas and to metastases. p16 was significantly decreased in primary tumors from melanoma patients who developed recurrent disease (P = .0000013). Cyclin D1 and pRb showed a progressive increase in expression from benign to malignant tumors but with relative decreases in the more advanced tumors (thick primaries and metastatic melanomas). Alterations in cell cycle proteins involved in G1/S transition are implicated in melanocytic tumor progression and have a potential role in diagnosis and prognostication.

LBA9084 Background: Adjuvant radiotherapy (RT) is an option for patients with isolated regional recurrence of melanoma considered to be at high risk of further regional recurrence after lymphadenectomy. This is the first completed study to assess the effects of RT on regional recurrence, survival, morbidity and quality of life (QOL) in these patients. Methods: Multicenter randomized study of patients with isolated regional recurrence at increased risk (>25%) of regional recurrence. Eligibile patients included ≥1 parotid, ≥ 2 cervical or axillary or ≥ 3 groin nodes or extra nodal spread of tumor or maximum metastatic node diameter ≥3cm in neck or axilla or ≥4cm in the groin. Patients were randomized to observation or regional nodal basin RT (48Gy in 20 fractions) after lymphadenectomy. Regional recurrence was the primary end point and morbidity, QOL, patterns of relapse, disease free and overall survival were secondary end points. The target sample size was 220 patients, which would enable a difference in 3 year regional relapse (cumulative incidence) rates of 30% versus 15% to be detected with a power of 80% (using a two sided logrank test at the 5% level of significance). Results: 250 pts were randomized from 16 centers from March 2002 to September 2007. There were 123 in the RT group and 127 in OBS group. 2 pts withdrew consent and 31 were excluded from analysis of the main objective following an independent blinded review of eligibility compliance by two reviewers. 227 pts were available for analysis of the main objective (109 RT, 108 OBS). Median follow-up was 27 mo. There was a statistically significant improvement in lymph node field control with radiotherapy, 20 RT pts and 34 OBS pts relapsed (HR 1.77 1.02–3.08 p=0.041). Median survival times were 2.6 years (RT) and 3.9 years (OBS) p=0.14. Conclusions: Adjuvant RT improved regional control in melanoma patients at high risk of regional relapse after lymphadenectomy. An effect on survival was not demonstrated. No significant financial relationships to disclose.

Our results show that ICP-MS analysis of antimony concentrations in FNB specimens from lymph nodes can accurately confirm the identity of SLNs. Used in conjunction with techniques such as proton magnetic resonance spectroscopy for the nonsurgical evaluation of SLNs, ICP-MS analysis of antimony concentrations in FNB samples could potentially serve as a minimally invasive alternative to surgery and histopathologic evaluation to objectively classify a given node as sentinel or nonsentinel and determine its tumor-harboring status.

9583 Background: Combination D+T improves the overall survival (OS) of patients (pts) with V600 BRAF-mutation positive advanced melanoma. D+T is currently being explored in an adjuvant study of pts with resected stage III melanoma (NCT01682083). We sought to explore neoadjuvant D+T for pts with bulky but resectable stage III melanoma (NCT01972347). Methods: In this phase 2 study, all pts received D (150 mg twice daily) + T (2 mg once daily) for 12 wks prior to complete resection of the pre-therapy tumour bed (RES), then 40 wks of further D+T. Eligible pts were ≥ 18 yrs, ECOG PS ≤ 1 with histologically confirmed resectable bulky stage IIIB/C BRAF V600E/K mutant melanoma. CT and PET scans were performed at baseline and 12 wks just prior to RES for RECIST and metabolic complete response (rCR and mCR respectively). CT monitoring was continued 12 wkly thereafter to 2 yrs then 6 mnthly to 3 yrs. Biopsies were taken at baseline and wk 1. The primary endpoints were the complete pathological response (pCR) and RECIST response rate (rRR) at wk 12. Secondary endpoints were surgical morbidity, mCR, relapse free survival (RFS), OS, toxicity and translational endpoints. Results: At data cut 4 Jan 2016, 19 had commenced D+T. 14 had reached RES (10 stage IIIC [2 in-transit only], 4 IIIB; 12 V600E, 1 V00K, 1 V600). At RES, 6/14 (43%) had pCR, 5/14 (36%) had rCR (rRR 93%), and 7/14 (50%) had mCR. All 6 pts with pCR had mCR, but 2 did not have rCR. No pt progressed during neoadjuvant treatment. 2/14 pts recurred in the resected field 12 and 36 wks after RES on D+T. These pts had the highest ctDNA at baseline. 8/14 (57%) had ≥ 1 surgical complication post RES; 8 had a wound infection requiring antibiotics, 5 had a seroma, 2 bled (1 wound evacuation). 11/14 had a post RES drain (median drain time 27d). 12/14 (86%) interrupted D+T in the first 12 wks for a median of 7d, 9 due to pyrexia ( ≥ 38.5oC). 1 pt ceased D+T at wk 28 due to renal failure. Conclusions: A high rate of pCR was observed with neoadjuvant D+T for resectable stage III melanoma. pCR correlated with mCR, but not rCR. Surgical complication rates were consistent with historic controls and stage of disease. The trial and translational research is ongoing, and ease of resection, RFS and OS data are being collected. Clinical trial information: NCT01972347.

Male gender is independently and significantly associated with poor prognosis in melanoma of all clinical stages. The biological underpinnings of this sex difference remain largely unknown, but we hypothesized that gene expression from gonosomes (sex chromosomes) might play an important role. We demonstrate that loss of the inactivated X chromosome in melanomas arising in females is strongly associated with poor distant metastasis-free survival, suggesting a dosage benefit from two X chromosomes. The gonosomal protein phosphatase 2 regulatory subunit B, beta (PPP2R3B) gene is located on the pseudoautosomal region (PAR) of the X chromosome in females and the Y chromosome in males. We observed that, despite its location on the PAR that predicts equal dosage across genders, PPP2R3B expression was lower in males than in females and was independently correlated with poor clinical outcome. PPP2R3B codes for the PR70 protein, a regulatory substrate-recognizing subunit of protein phosphatase 2A. PR70 decreased melanoma growth by negatively interfering with DNA replication and cell cycle progression through its role in stabilizing the cell division cycle 6 (CDC6)-chromatin licensing and DNA replication factor 1 (CDT1) interaction, which delays the firing of origins of DNA replication. Hence, PR70 functionally behaves as an X-linked tumor suppressor gene.

9581 Background: For several cancers, response to neoadjuvant therapy (NAT) correlates with survival. Targeted and immune therapies achieve high response rates and durable survival in many patients with metastatic melanoma. Their role as NAT for stage III disease is not clear, and whether pathological response following NAT correlates with relapse-free (RFS) or overall survival (OS) in melanoma is unknown. Methods: Pooled clinical data from four ongoing NAT clinical trials (NCT02437279, NCT02231775, NCT02519322, NCT01972347) at three large melanoma centers participating in the INMC were examined. All trials included only patients with surgically resectable clinical stage III melanoma. NAT regimens included dabrafenib/trametinib (DT) and nivolumab (nivo) [single agent or in combination with ipilimumab (ipi/nivo)]. Patients who had undergone surgery prior to 27 th January 2017 are included in this preliminary analysis. A pathological complete response (pCR) was defined as no viable melanoma cells in the resected specimen by hematoxylin and eosin evaluations by dedicated dermatopathologists. Results: 58 patients with clinical stage III melanoma (AJCCv7: 18 IIIB, 40 IIIC) have completed NAT and undergone surgery. 18 received neoadjuvant immunotherapy (IT): ipi/nivo x2 doses (N = 10), ipi/nivo x3 doses (N = 4) or nivo x4 doses (N = 4). 40 received neoadjuvant DT, either for two (N = 10) or three months (N = 30). Median age is 55 years (range 22-84). A pCR was observed in 50% of patients, 7 (39%) with IT and 22 (55%) with DT. Median follow-up is 10.2 months (95% CI 8.7-12.5). 14 (24%) patients have recurred (5 local, 8 distant, 1 both), 2 (11%) after IT, 12 (30%) after DT. For those with pCR, 14% have recurred, 0/7 (0%) after IT, 4/22 (18%) after DT. In contrast, for those without pCR, 34% have recurred, 2/11 (18%) after IT and 8/18 (44%) after DT. Two deaths have occurred, both after neoadjuvant TT. Early data suggests improved RFS in those with pCR. Conclusions: Neoadjuvant targeted and immunotherapy are active regimens in clinical stage III melanoma patients and are associated with high pCR rate. Preliminary data suggest pCR correlates with improved RFS. Updated data will be presented. Clinical trial information: NCT02437279, NCT02231775, NCT02519322, NCT01972347.

BNLMs tended to present at a more advanced stage, with thicker primary tumors, but had a metastatic pattern comparable to and was not more aggressive in behavior than other types of melanoma. The authors concluded that BNLMs should be treated in the same way as any other melanoma variants based on clinical staging and pathologic prognostic indices.

Murali, Rajmohan MBBS, FRCPA; Thompson, John F. MD FRACS, FACS; Scolyer, Richard A. MD FRCPA, FRCPath Author Information

Pigmented epithelioid melanocytoma (PEM) is a recently described entity encompassing epithelioid blue nevus (of Carney complex) and most tumors earlier considered as so-called "animal-type melanoma". Loss of expression of a Carney complex gene, cyclic adenosine 3',5' monophosphate-dependent protein kinase regulatory subunit 1alpha, is observed in the majority of PEMs. Initial reports with short-term follow-up have suggested that although PEMs frequently metastasize to lymph nodes, they have a more favorable outcome than conventional melanomas. In this report, we present the results of long-term follow-up in 26 patients with PEMs from North America and Australia. There were 9 males and 17 females, with a median age of 20 years. The tumors involved the trunk (6 cases), extremities (12 cases), genitalia (1 case), and the head and neck region (7 cases) had a median Breslow thickness of 2.2 mm (range 0.80 to 10.0 mm) and a median Clark level of 4. Eight of the patients developed lymph node metastases. After a median follow-up period of 67 months (range 39 to 216 mo), all patients are alive and free of disease. These findings provide further evidence that PEM is a unique low-grade melanocytic tumor with limited metastatic potential (to lymph nodes), but a favorable long-term clinical course.