Abstract B40: Intratumor heterogeneity in lung adenocarcinoma: Beyond genetics
Authors: Cajal Santiago Ramon y 
Published: May 2017

Background: For decades, pathologists have been describing new anatomopathological entities in lung carcinomas emphasizing the great heterogeneity of intratumor cell growth patterns. Modern genomic studies have identified a vast number of genetic alterations throughout the whole tumor and metastasis. In lung, oncogenic drivers such as EGFR, ALK, ROS, and RAS are mutated or translocated in a significant number of adenocarcinomas. Because genetic alteration can be heterogeneous, we studied DNA mutations and RNA expression in three different areas of the tumors, as well as protein expression of receptors and signaling factors in whole lung carcinomas sections.

Material and Methods: In 130 lung adenocarcinomas the histopathological features were assessed as well as the expression of ALK, HER2, ki67, pMAPK, mtor, 4E-BP1, p4E-BP1, eIF4E, peIF4E, and Epithelial-Mesenchymal Transition (EMT) factors (N-cadherin, YB1, pYB1) by specific antibodies in whole paraffin sections. Homogeneous expression was considered when &gt;80% tumor cells displayed a strong positivity. In 30 adenocarcinomas, molecular studies were run in three different histological cores with acinar, papilar and micropapilar cell growth patterns. DNA extraction for detection of mutations of EGFR and KRAS and RNA extraction, and gene expression of 110 genes was screened using NanoString technology.

Levels of expression were evaluated semi quantitatively as percentage and intensity of stained tumor cells (histo-score [H score]) and correlations were analyzed using Kruskal-Wallis and Kaplan-Meier (log Rank) statistical tests.

Results: The predominant histological subtypes were acinar, papillary and solid, with the latter associated with higher histological grade and more necrosis. p4E-BP1 and peIF4E displayed a homogenous and diffuse protein expression in about 80% of tumors. High expression of eIF4E, 4EBP1 and YB1 was associated with higher recurrence rate, histological grade and metastases. Regarding RNA expression, 90% of cases showed intratumoral heterogeneity in some genes. EGFR mutations show a heterogeneous distribution in about 20% cases while KRAS mutations were positive in all the areas of the tumors.

Conclusions: In lung adenocarcinomas, there is intratumor heterogeneity of mRNA expression in most cases, of EGFR mutations in a significant number of cases and a striking diversity in protein expression. With this data, several conclusions can be drawn: first, the importance to study several areas of the tumors to assess tumor heterogeneity both at molecular and protein levels; second, the patchy expression of signaling factors, probably due to local factors such as hypoxia, may explain partial clinical responses, third, in most cases peIF4E displayed a homogeneous expression supporting its role as a therapeutical target and fourth, pathologists need to integrate the molecular data, protein and histopathological data and apply systems biology and topologic approaches to highlight the more relevant prognostic information and therapeutical options for each tumor and patient.

Citation Format: Santiago Ramon y Cajal. Intratumor heterogeneity in lung adenocarcinoma: Beyond genetics. [abstract]. In: Proceedings of the AACR Special Conference on Translational Control of Cancer: A New Frontier in Cancer Biology and Therapy; 2016 Oct 27-30; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2017;77(6 Suppl):Abstract nr B40.