Differential expression of immunohistochemical markers in primary lung and breast cancers enriched for triple‐negative tumours

Aims In breast cancer patients presenting with a lung lesion, the distinction between lung and breast origin is clinically important. Lung and breast cancers are both CK 7 + / CK 20 − , so additional immunohistochemical markers are needed. Methods and results We examined the expression of oestrogen receptor ( ER ), progesterone receptor ( PR ), thyroid transcription factor‐1 ( TTF ‐1), gross cystic disease fluid protein‐15 ( GCDFP ‐15), p63 and Wilms’ tumour 1 ( WT 1) in a series of tissue microarrays comprising 266 non‐small‐cell lung cancers and 837 primary breast cancers enriched for triple‐negative tumours ( TNBC ). Staining for ER , PR , TTF ‐1 and GCDFP ‐15 was present in 63%, 49%, 0% and 25% of breast and 6%, 9%, 59% and 1% of lung cancers, respectively. Strong staining for p63 was present in 63 (97%) lung squamous cell carcinomas and only eight (9%) TNBC . WT 1 nuclear staining was rare; however, cytoplasmic staining was identified in 49 (40%) TNBC and 10 (5%) lung cancers. Cluster analysis segregated TNBC from lung cancers with TTF ‐1 and/or p63 staining favouring lung origin, and GCDFP ‐15 or WT 1 staining favouring breast origin. Cancers negative for all four markers (17%) were 60% breast and 40% lung origin. Conclusion An immunohistochemical panel incorporating ER , TTF ‐1, GCDFP ‐15, p63 and WT 1 can help to distinguish lung cancer from metastatic breast cancer, including TNBC .