From Lynete Sholl and colleagues: Pulmonary Large Cell Carcinoma Lacking Squamous Differentiation Is Clinicopathologically Indistinguishable From Solid-Subtype Adenocarcinoma

http://www.archivesofpathology.org/doi/pdf/10.5858/arpa.2013-0179-OA

David H. Hwang, David P. Szeto, Anthony S. Perry, Jacqueline L. Bruce, and Lynette M. Sholl (2013) Pulmonary Large Cell Carcinoma Lacking Squamous Differentiation Is Clinicopathologically Indistinguishable From Solid-Subtype Adenocarcinoma. Archives of Pathology & Laboratory Medicine In-Press.

Early Online Release

Pulmonary Large Cell Carcinoma Lacking Squamous Differentiation Is Clinicopathologically Indistinguishable From Solid-Subtype Adenocarcinoma

David H. Hwang , MD; David P. Szeto , BS; Anthony S. Perry , MD; Jacqueline L. Bruce , PhD; Lynette M. Sholl , MD

From the Department of Pathology (Drs Hwang, Bruce, and Sholl and Mr Szeto) and

Center for Advanced Molecular Diagnostics (Mr Szeto and Drs Bruce and Sholl), Brigham and Women's Hospital, Boston, Massachusetts;

Harvard Medical School, Boston, Massachusetts (Drs Hwang and Sholl); and

the Department of Pathology, Banner MD Anderson Cancer Center, Gilbert, Arizona (Dr Perry).

Context.—Pulmonary large cell carcinoma (LCC) includes tumors not readily diagnosed as adenocarcinoma (ADC) or squamous cell carcinoma on morphologic grounds, without regard to immunophenotype, according to the World Health Organization (WHO). This ambiguous designation may cause confusion over selection of mutation testing and directed therapies. Several groups have proposed the use of immunohistochemistry (IHC) to recategorize LCC as ADC or squamous cell carcinoma; however, it remains unclear if strictly defined LCCs are a clinicopathologically distinct lung tumor subset.

Objective.—To compare the pathologic, molecular, and clinical features of 2 morphologically similar tumors: solid-subtype ADC and LCC.

Design.—Tumors were included on the basis of solid growth pattern; tumors with squamous or neuroendocrine differentiation were excluded. Solid ADC (n = 42) and LCC (n = 57) were diagnosed by using WHO criteria (5 intracellular mucin droplets in ≥2 high-power fields for solid ADC) and tested for KRAS, EGFR, and ALK alterations.

Results.—Both solid ADC and LCC groups were dominated by tumors with “undifferentiated”-type morphology and both had a high frequency of thyroid transcription factor 1 expression. KRAS was mutated in 38% of solid ADCs versus 43% of LCCs (P = .62). One ALK-rearranged and 1 EGFR-mutated tumor were detected in the solid ADC and LCC groups, respectively. There were no significant differences in clinical features or outcomes; the prevalence of smoking in both groups was greater than 95%.

Conclusions.—Other than a paucity of intracellular mucin, LCC lacking squamous or neuroendocrine differentiation is indistinguishable from solid-subtype ADC. We propose the reclassification of these tumors as mucin-poor solid adenocarcinomas.