Stromal micropapillary predominant lung adenocarcinoma: A rare histological phenotype with poor prognosis

Abstract

An extremely rare case of stromal micropapillary predominant lung adenocarcinoma is presented in this study. A 70-year-old woman visited our hospital because of an abnormal shadow on chest X-ray. Chest computed tomography revealed a nodule in the left lower lobe and a mass in the left upper lobe. She underwent an exploratory thoracotomy owing to the suspicion of advanced lung cancer. Pathological examination of the left lower lobe nodule revealed tumour cells with more than half the tumour cells showing stromal micropapillary pattern (SMP), consisting of tumour cells invading the fibrotic stroma. In general, micropapillary adenocarcinomas in the lung form an aerogenous micropapillary pattern (AMP), in which tumour cells float in alveolar spaces. Because the prognosis of SMP lung adenocarcinomas is known to be worse than that of AMP lung adenocarcinomas and have a high frequency of epidermal growth factor receptor mutations, the discrimination of SMP from AMP is important for both pathologists and clinicians.

Expansion of the Concept of Micropapillary Adenocarcinoma to Include a Newly Recognized Filigree Pattern as Well as the Classical Pattern Based on 1468 Stage I Lung Adenocarcinomas

“…The classical MIP pattern was defined as (1) a floret pattern with tumor cells growing in papillary tufts forming florets that lack fibrovascular cores and a (2) stromal pattern with tumor cells invading stromal spaces encased by connective tissues. 4,5,22,23,26 Figure 1. Concept of the filigree pattern.…”

“…5,21 Although a stromal pattern of MIP adenocarcinoma was not illustrated in the WHO classification, the common finding of stromal invasion was recognized 5 and the stromal MIP pattern is well documented to be associated with poor prognosis. 22,23 Therefore, in this article we have regarded the classical MIP pattern as including both the floret and stromal patterns.…”

Identification of filigree pattern increases the diagnostic accuracy of micropapillary pattern on frozen section for lung adenocarcinoma

“…If any discrepancies were noted in the histologic evaluation among pathologists, discussion was necessary to reach a consensus through the use of a multihead microscope. Based on the 2015 World Health Organization (WHO) classification, 21 the MIP structure was defined as (i) tumour cells growing in papillary tufts forming florets that lack fibrovascular cores, which may appear detached from and/or connected to alveolar walls; (ii) ring‐like glandular structures, which may float within alveolar spaces; and (iii) MIP adenocarcinoma, which can also show a stromal invasive pattern 22,23 …”

“…Based on the 2015 World Health Organization (WHO) classification, 21 the MIP structure was defined as (i) tumour cells growing in papillary tufts forming florets that lack fibrovascular cores, which may appear detached from and/or connected to alveolar walls; (ii) ring-like glandular structures, which may float within alveolar spaces; and (iii) MIP adenocarcinoma, which can also show a stromal invasive pattern. 22,23 The morphological spectrum of the MIP pattern was recently expanded to include a filigree pattern. The filigree pattern was defined as (i) tumour cells growing in delicate, lace-like, narrow stacks; (ii) the stacks of tumour cells lack fibrovascular cores; (iii) the stacks of tumour cells may be attached to alveolar walls; and (iv) the stacks of tumour cells consisted of at least three tumour cells above the basal tumour cell layer.…”