Genetic Analysis of Second Primary Lung Cancers in Patients Surviving Small Cell Lung Cancer1

We performed genetic analysis on 12 second primary non-small cell lung cancers in patients surviving small cell lung cancer to assess the potential contribution of smoking to the development of these tumors. Mutations of TP53 were found in three (25%) tumors, KRAS2 in three (25%) tumors, and CDKN2 in two (18%) tumors. Four (50%) mutations (one each in TPS3 and CDKN2 and two in KRAS2) were G:C to T:A transversions on the coding strand, a mutation accounting for approximately one-third of mutations in smoking-related tumors but uncommonly found in lung cancers not associated with smoking. The genetic changes in these second lung cancers are more representative of smokingassociated malignancies than lung cancers arising in patients occupationally exposed to irradiation and atomic bomb survivors. Introduction Combined chemotherapy and chest radiotherapy has been increasingly used over the past 2 decades for patients with SCLC3 because it prolongs survival compared to chemotherapy alone ( 1 ). Patients treated with chest radiotherapy have been found to have a 4-fold greater risk of developing a second cancer compared to patients treated with chemotherapy alone (2). More recently, combined chemotherapy and chest radiotherapy for patients with locally advanced non-SCLC and adjuvant systemic chemotherapy and breast irradiation for patients with localized breast cancer have been more commonly used. Second primary tumors are likely to be seen with increasing frequency Received 3/8/96: revised 4/I 7/96: accepted 4/I 8/96. I This is a U.S. government work: there are no restrictions on its use. The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of the Navy or the Department of Defense. 2 To whom requests for reprints should be addressed. at National Cancer Institute-Navy Medical Oncology Branch. Building 8. Room 5101. 8901 Rockville Pike. Bethesda. MD 20889-5 105. Phone: (301 ) 496-0929: Fax: (301) 496-()047. 3 The abbreviation used is: SCLC. small cell lung cancer. in these patients who have multiple risk factors ftr the development of second cancers. SCLC is the histological subtype of lung cancer most strongly associated with smoking. Patients surviving 2 years after SCLC are at risk for death from recurrent SCLC. second primary cancers, and other nonmalignant. smoking-related diseases. Lung cancer is the most common second primary cancer in these patients (2). Two-year cancer-free survivors of SCLC have a 10-fold increased risk of lung cancer. and this risk increases to 24-fold after 10 years from diagnosis (2). In addition to smoking, survivors of SCLC have additional potential risk factors for lung cancer, including treatment-related factors (chemotherapy and frequently chest radiotherapy), as well as possible genetic predisposition. Approximately one-third of mutations of the TP53 gene and the R4S gene family in lung cancer are G:C to T:A transversions on the coding strand (3). This change is thought to be due to the mutagenic action of components of tobacco smoke (3). Cancers not associated with smoking, including lung cancer in nonsmokers, uncommonly have these changes (3). Additional genetic loci have been found to be altered in lung cancer, including the CDKN2 gene (4), and have a similar pattern of point mutations as found in TP53 and the RAS gene family. Analysis of multiple genetic loci provides more data than analysis of a single locus from the same number of tumor samples. We have performed genetic analysis of five loci in second primary lung cancers of patients surviving SCLC to determine whether mutations in these cancers are characteristic of those attributed to smoking. Patients and Methods Among 6 1 1 2-year cancer-free survivors of SCLC included in the North American cohort study, 50 patients developed non-SCLC (2). An additional patient developed non-SCLC since the time of the original report. Nineteen tumors were available, and of these, 12 samples contained amplifiable DNA sufficient for genetic analysis. Clinical information was available for these 12 patients. Tumor samples of the initial SCLCs were available from two patients. DNA extracted from formalinfixed, paraffin-embedded tissues was screened for mutations of TP53 ADDIN ENRef (5) and CDKN2 ADDIN ENRef (4) using PCR-single strand conformation polymorphism and mutations of codon 12 or 13 of KRAS2, HRASJ, and NRAS using PCRRFLP (5). Samples containing mutations were subjected to DNA sequence analysis (5). Statistical significance of comparisons was analyzed using the two-sided Fisher’s exact test. Results and Discussion There were I 0 men and 2 women; median age at diagnosis of SCLC was 59 years (range, 46-60 years). Ten patients had limited stage. All patients were initially treated with multiagent chemotherapy. and 10 had received chest radiotherapy. The median canResearch. on April 13, 2017. © 1996 American Association for Cancer clincancerres.aacrjournals.org Downloaded from 1104 Genetic Analysis of Second Lung Cancers Table I Characteristics of 12 patients developing second primary lung cancers after SCLC