ECP 2022 Abstract Book

Virchows Archiv (2022) 481 (Suppl 1):S1–S364 13 E-PS-15-017 Monitoring PIK3CA molecular heterogeneity in breast cancer using liquid biopsy P. Santiago Díaz*, I. Vázquez, L. Comerma, L. Camacho, R. Lon- garón, S. Servitja, B. Lloveras, B. Bellosillo, S. Clavé *Pathology Department, Hospital del Mar, Barcelona, Spain Background & objectives: Breast cancer is a dynamic disease with continuous clonal selection reflecting singular molecular alterations. This heterogeneity occurs intratumor and even among primary tumours and metastases. This study aimed to assess the role of liquid biopsy for monitoring molecular alterations. Methods: A 54-year-old woman with infiltrating lobular breast carcinoma was treated with neoadjuvant chemotherapy, radical mastectomy and hormone therapy. Disease was controlled for five years until increased levels of biochemical markers (CEA and Ca15.3) led to the detection of bone metastasis. Molecular charac- terization of the primary tumour identified H1047R mutation on PIK3CA, which was subsequently followed by digital PCR (dPCR). Results: Among liquid biopsies, PIK3CA H1047R allelic fraction (AF) remained at low levels and became undetectable during five years. However, disease progressed with elevated tumour markers, new bone lesions and skin metastases. This evident miscorrelation prompted new genomic characterizations. Next generation sequenc- ing (NGS) on a skin lesion showed mutations on TP53 and ERBB2, but no alterations on PIK3CA. NGS analysis on plasma samples revealed three new PI3KCA mutations (E545K with the highest AF, E542K and E726K) and three TP53 mutations. We then performed new dPCR targeting PIK3CA E545K mutation on stored liquid biopsies. This mutation, while not predominant, was the one that correlated best with biochemical and clinical evolution. Conclusion: Digital PCR on cell free plasma samples allows continuous monitoring of the evolving molecular alterations but do not completely reflect tumour heterogeneity. Clonal dynamics constitutes a major challenge during cancer follow-up, that can be assessed, despite the higher cost, by NGS of plasma or tissue samples. E-PS-15-018 Assessment of EGFR mutation status in Tunisian series of non- small cell lung carcinomas M.A. Mezni, M. Ben Rekaya, F. Sassi*, L. Bel Hadj Kacem, R. Aloui, N. Ben Othman, A. Bani, M. Ksentini, N. Znaidi, S. Rammeh *Habib Thameur Hospital, Pathology Department, Tunisia Background & objectives: The epidermal growth factor receptor (EGFR) activating oncogenic mutations are detected in 20% of non- small cell lung carcinomas (NSCLC) and are encountered in exons 18 to 21. We aimed to report the frequency and types of these mutations in our practice. Methods: EGFR mutation status of 75 formalin-fixed and paraffin- embedded samples of NSCLC was assessed. Mutational analysis concerned exon 18-21 by the ARMS-Scoprion real-time PCR tech- nique using the Therascreen EGFR RGQ PCR mutation kit allow- ing the detection of 29 somatic mutations in the EGFR gene. Results: Average age was 55 years with a male predominance (63%). Adenocarcinoma was the most common histological type (93%), followed by squamous cell carcinoma (6%) and adenosqua- mous carcinoma (1%). Molecular analysis showed that 23% (17 cases) had one or two mutations. Del-exon19, L858R and Insertion were observed with respective frequencies of 65% (11 cases), 23% (4 cases) and 6.67% (1 case). Only one case presented a concomi- tance of two mutations: L858R and the resistance mutation TKI T790M. Of the mutated cases, 65% (11/17 cases) were female and 94% (16/17 cases) were adenocarcinoma. Conclusion: The frequency of mutated cases is slightly higher than the frequency already described in a previous study by our team (11.5%) but close to the frequency of mutated cases in the Cauca- sian population (16%). The most frequent activating mutations are deletions of exon 19 and the L858R mutation of exon 21, the two representing 90% of activating mutations. E-PS-15-019 About a gastric GIST with co-occurrence of mutations in exons 9 and 11 of the c-kit gene F. Sassi*, M. Ben Rekaya, F. Ksontini, A.M. Hmayeda, L. Bel Hadj Kacem, R. Aloui, M. Ksentini, M. Trabelsi, A. Blel, N. Znaidi, S. Rammeh *Department of Pathology, Charles Nicolle Hospital Tunis, Tunisia Background & objectives: The co-occurrence of two or more muta- tions in the same oncogene in gastrointestinal stromal tumours (GISTs) is rare and complete pathological response after neoadjuvant treatment with Imatinib is rare. Methods: We report the case of a 41-year-old woman presenting with abdominal pain. Radiological explorations revealed a gastric mass of 10.5 cm. The histological examination of a biopsy speci- men concluded to a GIST. The tumour was locally advanced. The patient had neoadjuvant treatment with Imatinib. Four months after the treatment, the patient was operated with a complete pathologi- cal response. Results: Extraction of DNA was done by Qiagen kit from 4 sections of 10 μm FFPE biopsies. The five hot spot regions comprising the exons and their flanking regions of the KIT gene (9, 11 and 17) and PDGFRA (12 and 18) were analysed. A co-occurrence of 6 coding variations in the KIT gene was observed. Exon 9 indicates the presence of a missense p varia- tion. Ala502Asp which has never been described. On exon 11, five mutations were found, including 2 known (Leu576Pro and Pro577Ser) and 3 others (Gln575Pro, Thr574Pro and Pro577Pro) not described. All variations at exon 17 and exon 12 of PDGFRA were polymorphisms. Conclusion: Our case showed a concomitance of mutations of exons 9+11 of the KIT gene in a gastric GIST; this co-occurrence is rare and its impact on the response to Imatinib is little known. Pathological complete response is rare in GISTs and generally associated with exon 11 mutations affecting codons 557 and 559, our case carries variations affecting codons 574, 575, 576 and577, plus exon 9 mutation in codon 502. This co-occurrence may be the factor responsible for this good response. E-PS-15-020 Liquid biopsy: new technical approaches to tumour evaluation G. Smagulova*, S. Yessentayeva, A. Tulepbayeva, Z. Ilyanova, N. Nurgaliev *Diagnostic laboratory “GammaLab”, Kazakhstan Background & objectives: Understanding the potential and limitations molecular profiling of tumour based on CTC and ctDNA important for patient stratification. These new tools for diagnosis and prognosis of cancer gives us insight of tumour heterogeneity and evolution, which improves cancer treatment strategies. Methods: Total of 21 patients were examined by LB. 13 of them with CRC, 5-NSCLC, 3-melanoma. All patients S309