Search

In lung adenocarcinoma, canonical EML4-ALKinversion results in a fusion protein with a constitutively active ALK kinase domain. Evidence of ALKrearrangement occurs in a minority (2–7%) of lung adenocarcinoma, and only ~60% of these patients will respond to targeted ALK inhibition by drugs such as crizotinib and ceritinib. Clinically, targeted anti-ALK therapy is often initiated based on evidence of an ALKgenomic rearrangement detected by fluorescence in situhybridization (FISH) of interphase cells in formalin-fixed, paraffin-embedded tissue sections. At the genomic level, however, ALKrearrangements are heterogeneous, with multiple potential breakpoints in EML4, and alternate fusion partners. Using next-generation sequencing of DNA and RNA together with ALK immunohistochemistry, we comprehensively characterized genomic breakpoints in 33 FISH-positive lung adenocarcinomas. Of these 33 cases, 29 (88%) had detectable DNA level ALK rearrangements involving EML4, KIF5B, or non-canonical partners including ASXL2, ATP6V1B1, PRKAR1A, and SPDYA. A subset of 12 cases had material available for RNA-Seq. Of these, eight of eight (100%) cases with DNA rearrangements showed ALK fusion transcripts from RNA-Seq; three of four cases (75%) without detectable DNA rearrangements were similarly negative by RNA-Seq, and one case was positive by RNA-Seq but negative by DNA next-generation sequencing. By immunohistochemistry, 17 of 19 (89%) tested cases were clearly positive for ALK protein expression; the remaining cases had no detectable DNA level rearrangement or had a non-canonical rearrangement not predicted to form a fusion protein. Survival analysis of patients treated with targeted ALK inhibitors demonstrates a significant difference in mean survival between patients with next-generation sequencing confirmed EML4-ALKrearrangements, and those without (20.6 months vs5.4 months, P<0.01). Together, these data demonstrate abundant genomic heterogeneity among ALK-rearranged lung adenocarcinoma, which may account for differences in treatment response with targeted ALK inhibitors.

Rare breast neoplasms resembling the tall-cell variant of papillary thyroid carcinoma have been reported. In addition, papillary carcinoma of the breast occasionally displays nuclear features reminiscent of papillary thyroid carcinoma. In this study, we evaluated 33 intraductal/intracystic papillary carcinomas of the breast for the presence and extent of nuclear overlap, grooves, clearing, and inclusions, as well as features of the tall-cell or columnar-cell variants of papillary thyroid carcinoma. RETrearrangements were assessed in a subset of these cases. Paired probes localizing to the centromeric and telomeric ends of the RETgene on chromosome 10 were used for FISH using a break-apart approach. Single round and nested PCR was performed to detect RET/PTC1, RET/PTC2, RET/PTC3and ELKS-RETfusion transcripts. Nuclear overlap, grooves, stratification, and clearing were identified in 24 (73%), 14 (42%), 11 (33%), and 9 (27%) cases respectively, whereas nuclear inclusions and ‘tall-cell’ features were each seen in only one (3%) and two (6%) cases, respectively. Four of 19 tested cases displayed split FISH signals in a low percentage of cells and were considered borderline for RETrearrangement. All 19 tested cases with amplifiable RNA were negative for the four RETfusion transcripts evaluated by RT-PCR. Although papillary carcinomas of breast often display one or more cytoarchitectural features of papillary thyroid carcinoma, there is no evidence that RETrearrangements are involved.