Stromal micropapillary pattern predominant lung adenocarcinoma - a report of two cases

A new lung adenocarcinoma classification has been proposed by the International Association for the Study of Lung Cancer, American Thoracic Society and European Respiratory Society (IASLC/ATS/ERS). In this classification, the micropapillary subtype of lung adenocarcinoma (MSLA) was recommended as a newly added subtype of lung adenocarcinoma to lepidic, acinar, papillary, and solid subtypes defined in the 2004 World Health Organization (WHO) classification [1,2]. Generally, the micropapillary pattern is defined as tumor cells growing in papillary tufts, which lack fibrovascular cores surrounded by lacunar spaces and has been reported to be associated with a high incidence of nodal metastasis and poor prognosis [3-6]. This pattern has been described in various organs such as breast [7,8], urinary bladder [9,10], ovary [11,12], salivary gland [13], and is known to behave aggressively. In other organs than the lung, this pattern was observed mainly in stroma as invasive components (stromal micropapillary pattern: SMP) [7-19]; however in lung, MSLA is widely recognized as floating tumor cells within alveolar spaces (aerogenous micropapillary pattern: AMP) [3,4].We examined whether SMP predominant subtypes were present in lung adenocarcinoma. During the period from February 2007 to December 2010, 559 patients with lung adenocarcinoma were consecutively treated by surgical resection at the Kanagawa Cancer Center, Kanagawa, Japan, and we found only two cases of SMP predominant lung adenocarcinoma (SMPPLA) (0.36%). We reported the cases of SMPPLA and attempted to describe the clinicopathological features.A 49-year-old Japanese man was referred to the hospital with lung adenocarcinoma, which was diagnosed by the transthoracic needle biopsy. A computed tomography (CT) scan detected a 32 mm-sized localized solid tumor in the right upper lobe and swelling of the mediastinal lymph node (Figure 1a). He was an ex-smoker and admission laboratory tests showed increased carcinoembryon