Lepidic adenocarcinoma describes tumour growth along intact alveoli with stromal invasion only pathologically and is defined as an adenocarcinoma in situ (AIS) or a minimally invasive adenocarcinoma (MIA). It is associated with a good prognosis with 98% 5-year survival after surgical resection. Its CT appearance can vary from a ground glass nodule to part-solid lesions with bubble-like internal lucencies. It is a slow-growing tumour and is frequently multifocal or bilateral.
The IASLC/ATS/ERS classification system defines four histologic prognostic groups for non-small cell lung cancer (NSCLC): adenocarcinoma in-situ (AIS), invasive adenocarcinoma of the non-micropapillary type (MIA), invasive adenocarcinoma with micropapillary growth (miPa) and invasive adenocarcinoma displaying predominantly lepidic growth (iLPA). However, the probability of recurrence after surgical resection is not equal between the different histologic prognostic groups.
In a recent study, we analysed surgical resection specimens with a histologic diagnosis of lepidic adenocarcinoma. The specimens were grouped according to their histologic subtype: papillary predominant, solid predominant, lepidic predominant and micropapillary predominant. We compared the probability of recurrence-free survival (RFS) between these groups and found that the acinar predominant subtype had a significantly higher RFS than the other histologic prognostic groups.
Considering the histologic differences in prognosis between the groups, it is important to determine which morphologic subtypes are associated with a better prognosis and can inform clinical management.
Although lobectomy is the standard procedure for resectable LUAD, sublobar resection has been suggested in patients with a lepidic predominant pattern on histology, especially in those over 75 years of age. However, this approach may be associated with a higher risk of metastatic spread, as well as the possibility of subsegmental lymph node involvement.
A retrospective 2-year review of surgical resection specimens at our institution was performed. Thirty-four cases were identified and classified as adenocarcinoma in-situ, MIA or iLPA on histopathology. Of these, 16 were unifocal and 23 were multicentric with a solitary nodule presentation on computed tomography (CT).
A pure ground-glass-like (GGO) lesion corresponded to AIS in the majority of cases and a part-solid lesion to MIA or iLPA. In most cases, the diagnosis of adenocarcinoma in-situ or MIA was established on CT-guided core biopsy using a trucut 20-gauge needle. During the follow-up period, 24 recurrences were recorded: 2 local recurrences and 22 distant metastases. Two patients developed post-procedural haemoptysis. The most common site of recurrence was the mediastinum (49%). The most frequent cause for recurrent disease was metastatic disease with the remainder due to local recurrence or respiratory symptoms. It is therefore important to accurately identify the underlying malignant lesion by a judicious CT-guided biopsies in order to ensure that only resectable tumours are removed from the lungs of these patients. In addition, every effort should be made to biopsy the solid component of a part-solid nodule as this is the area that represents invasive growth and can lead to misdiagnosis as a pre-invasive lesion. The authors would like to thank Mrs. Sandra M. Cairns for her assistance with obtaining patient records.
