Background
Adenosquamous carcinoma (ADSC) of the lung, a rare but aggressive subtype of non-small cell lung cancer (NSCLC), is defined as a carcinoma containing components of adenocarcinoma (ADC) and squamous cell carcinoma (SqCC). Mutations of epidermal growth factor receptor (EGFR) are found at a frequency of 15 to 44% in Asian ADSC, and EGFR tyrosine kinase inhibitors (EGFR-TKIs) are a more effective treatment for EGFR-mutated ADSC compared to chemotherapy. However, ADSC in small lung biopsies could be misdiagnosed as SqCC or non-small cell carcinoma (NSCC) favor SqCC due to undersampling, which may result in neglecting of
EGFR
mutation testing and affecting patients’ clinical management, particularly in Asian patients that relatively have high prevalence of
EGFR
mutation.
Methods
A total of 148 small lung biopsy cases with pathological diagnosis of SqCC or NSCC favor SqCC were retrospectively enrolled. The frequency of
EGFR
mutations and the correlation between patients’
EGFR
mutation status and clinicopathological characteristics were evaluated.
Results
EGFR
mutations were found in 8.8% (13 /148) of all cases with 5.2% (7/135) in SqCC and 46.2% (6/13) in NSCC favor SqCC. There were 7 (53.8%) L858R mutation, 4 (30.8%) exon 19 deletions, and 2 (15.4%) cases with coexistent L858R and T790 M mutations. Multivariate analysis showed that
EGFR
mutations were more prevalent in never-smokers (83.3% versus 16.7%,
p
= 0.006) and patients diagnosed as NSCC favor SqCC (46.2% versus 5.2%,
p
= 0.001). Moreover, 75% (3/4) of
EGFR
mutation-positive cases with subsequent surgical resection or rebiopsy were further diagnosed as ADSC.
Conclusions
EGFR
mutation testing should be performed in Asian patients with SqCC diagnosed from small lung biopsies, especially in never-smokers and patients with diagnosis of NSCC favor SqCC, which have a high probability of being ADSC.