Table 1.
Clinicopathologic Characteristics of Patients
Figure 1.
Immunohistochemical findings of ROS1-rearranged tumors.
An ROS1-rearrangned tumor showed strong and diffuse cytoplasmic staining (a) (inset: ROS1 FISH with split signals). Other tumors showed cytoplasmic staining with membrane accentuation (b), membranous staining with weaker cytoplasmic intensity (c), or cytoplasmic or paranuclear aggregates (d).
Figure 2.
Immunohistochemical findings of ROS1-non-rearranged tumors.
Most ROS1-non-rearranged tumors showed no immunoreactivity, or focal and patchy staining with weak intensity (a, b) (inset: ROS1 FISH without split signals). One tumor showed strong and diffuse staining pattern, which is similar to that of rearranged tumors (c). ROS1 is occasionally expressed in surrounding type II pneumocytes (d).
Figure 3.
Representative photos from ALK IHC.
An ALK-rearranged tumor shows strong and diffuse staining (a) (inset: ALK FISH with split signals). In contrast, an ALK-non-rearranged tumor shows weak and patchy staining (b) (inset: ALK FISH without split signals).
Figure 4.
Comparison of the H-score and extent of ROS1 (a, b) and ALK (c, d) immunoreactivity in gene-rearranged vs. non-rearranged tumors.
Scatter dot plots for H-scores (a, c) and percentage of immunoreactive cells (b, d) show significantly increased expression of each protein in rearranged tumors (p<0.001). All rearranged tumors show an H-score of more than 100 and extent of more than 75%.
Table 2.
Diagnostic performance of IHC to predict gene rearrangement according to cutoff in both patient cohorts
Figure 5.
Comparison of the H-score in ROS1-non-rearranged tumors according to smoking history.
The scatter dot plot shows that the ROS1 protein is more expressed in tumors of smokers' than in those of never-smokers (p = 0.003).
Table 3.
Clinicopathologic Characteristics of ROS1 and ALK-rearranged adenocarcinomas
Figure 6.
Proposed diagnostic algorithm using ROS1 and ALK IHC.
When the tumor shows moderate to strong, or diffuse staining on IHC, FISH is recommend to confirm gene rearrangements. *The criteria should be determined based on each institutional method. According to this present study, subsequent FISH analysis is recommended for cases with an H-score ≥100, extent ≥75%, or the presence of intensity 2+ or 3+.
Figure 7.
Heterogeneity of histology and immunohistochemical staining.
One area of a ROS1-rearranged tumor shows a solid area with intense immunostaining for ROS1 (a and c). Another area shows a predominantly signet ring cell feature with weaker immunostaining (b and d). Both areas were ALK IHC-negative (e and f).