Material and Method: A total of 12 patients with a diagnosis of primary lung adenocarcinoma were included in the study. Twelve pathologists from eight study centers were asked first to determine the dominant histological pattern in these cases and then to decide whether the final diagnosis was in situ, minimally invasive or invasive adenocarcinoma.
Results: The kappa value for the agreement in determining the dominant pattern among the pathologists was 0.36 (p<0.001), with the values for the lepidic, acinar, papillary, solid, micropapillary patterns and mucinous character of adenocarcinoma being 0.34, 0.28, 0.30, 0.80, 0.16 and 0.38 respectively (p<0.001, p<0.001, p<0.001, p<0.001, p<0.001, p<0.001). None of the cases was diagnosed as in situ adenocarcinoma. On the other hand, the kappa value for the agreement in differentiating minimally invasive from invasive adenocarcinoma among reviewers was 0.17 (p<0.001).
Conclusion: The agreement among pathologists in determining the subtype of lung adenocarcinomas that depends on the identification of the dominant pattern was at intermediate level. In addition, the agreement in deciding whether the case is minimally invasive or invasive, was at low level. The criteria defining the histological patterns should be clarified and described in more detail. Educational activities and larger multicenter studies might be helpful in improving the agreement and standardization.
Table I: *IASL C/ATS /ERS Classification of Lung Adenocarcinoma
In this study, we aimed to investigate the interobserver agreement in terms of the dominant histological AC pattern and final diagnosis of AC.
The study included a total of 12 pathologists from eight institutions who specialized in lung pathology. The samples were evaluated under light microscopy according to the histologic criteria specified in the 2011 IASL C/ATS / ERS international multidisciplinary classification of lung adenocarcinoma consensus[5]. The reviewers were asked to determine the dominant AC pattern, presence of mucinous character and final diagnosis in each case. Adenocarcinoma patterns were lepidic, acinar, papillary, solid, micropapillary as described in the IASL C/ATS /ERS report. They were also asked to decide whether the case is a minimally invasive adenocarcinoma (MIAC) or an invasive adenocarcinoma (IAC) according to the morphology and the diameter of the invasive focus.
To determine the interobserver agreement among dominant patterns (lepidic, acinar, papillary, solid, micropapillary and mucinous), and between IAC and MIAC the results were evaluated using Fleiss kappa statistics (StataCorp. 2011, Stata Statistical Software: Release 12, College Station, TX, USA, StataCorp LP). The meaning of kappa values representing agreement among observers is presented in Table II[8].
Figure 1: The distribution of adenocarcinoma diagnoses.
Figure 3: The dominant histological patterns in the cases.
Table III: Kappa values of the histological patterns
The agreement in establishing stromal invasion was 100% and none of the cases were diagnosed as in situ AC. However, the agreement for the IAC and MIAC among reviewers was low level (kappa=0.17; p<0.001).
Various studies exist that have discussed relatively high reproducibility of histological subtyping of lung ACs[9,10]. However, there are also some other studies suggesting that the level of agreement is low for determining subtypes because of differentiation and the complex heterogeneous framework[11,12]. The main reason for this lies in the interlaced lepidic, acinar, and papillary patterns in the absence of desmoplasia. In addition, differentiating micropapillary and lepidic patterns from papillary may also be problematic; the classification requires that lepidic growth in the alveolar space filled with papillary structures should be considered as papillary AC in the absence of myofibroblastic stroma[5,13]. These studies suggest that the differential diagnosis of the patterns (especially lepidic, acinar and papillary) is still open to discussion. On the other hand, the solid pattern, which consists of lined-up tumor cells without a definite frame and space, shows the highest rate of agreement[14]. In the present study, weak and intermediate agreement was detected in patterns other than the solid subtype; our results were similar to other studies. Noguchi and Warth reported that education programs performed with the assistance of experienced pathologists have increased the agreement. However, the fact that their results did not reach perfect levels indicates that further studies are needed involving larger series with non-randomized cases[14,15].
Our study showed that the level of agreement in differentiating IAC form MIAC is low. Not only detecting the cells invading the stroma individually but also presence of any pattern other than lepidic defines invasion[5]. As explained above, when there is no desmoplasia due to the difficulty in differentiating patterns, measuring the magnitude of invasive focus under this complex frame is technically challenging[16].
The main limitation of our study was the low number of cases. In addition, the selected cases were indeed difficult to subtype. In studies performed on tumors with typical morphology, high levels of agreement were reported when compared with the agreement rates in problematic cases[9]. Furthermore, the study was of a single-step design and had no reference pathologist.
When determining the subtype of lung ACs in this study, we observed an intermediate level of agreement in identifying different patterns and a weak level of agreement in the diagnosis of MIAC. Our findings indicate that further studies are necessary and the classification criteria should be described in more detail to clarify some possible miscategorizations that currently exist. Educational activities and larger multicenter studies might be helpful for standardization.
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