Prevalence of ALK translocations in a large cohort of non-small cell cancer patients and quality of hybridization by sampling method

Introduction: Molecular analysis is frequently performed in small tissue or cytologic samples obtained by minimally invasive techniques. Unlike EGFR mutations, which can be analyzed by PCR from stained slides, ALK translocations are commonly identified by a complex technique known as fluorescent in situ hybridization (FISH). Not all samples may be adequate for this type of analysis. Materials & Methods: We studied the prevalence of ALK translocations identified by FISH in a large University Hospital cohort of 1002 samples from non small cell lung carcinoma patients. The study aimed to determine the performance of FISH testing on different diagnostic samples. Results: FISH was attempted in 1002 samples, including 195 surgical biopsies, 518 conventional bronchoscopies, 239 EBUS procedures, and 50 percutaneous transthoracic biopsies. The overall prevalence of ALK translocations was 3.5%. Hybridization failure occurred in 7.7% of the samples. 86.7% of the samples were ALK-, and 2.1% of the samples were inadequate for FISH due to a paucity of tumor cells. The vast majority of tissue samples obtained by bronchoscopy (97%) and surgery (98%) were adequate for FISH. Succesful molecular analysis on samples obtained by EBUS and percutaneous CT guided biopsy was possible in 73% and 74% of those samples respectively. Failed ALK translocation analysis was due to either hybridization failure or paucity of tumor cells. Conclusions: Molecular analysis of ALK translocations is feasible in a variety of samples, although hybridization failure or a paucity of tumor cells can be a problem in samples obtained by minimally invasive methods.