Malignant myxoid endobronchial tumour: a report of two cases with a uniquehistological pattern

Aims: To present two cases of malignant endobronchial myxoid tumours with a highly distinctive sarcomatoid pattern not previously described at this si te, and discuss their histogenesis in relation to previously documented end obronchial neoplasms. Methods and results: Both tumours presented in young adult females and were purely sarcomatoid with interweaving cords of small uniform, rounded or sl ightly elongated cells lying within a myxoid stroma. The stroma was alcian blue positive, but sensitive to hyaluronidase in both cases. The tumour cel ls contained a small Volume of periodic acid-Schiff-positive eosinophilic c ytoplasm and stained positively for vimentin only, but there also was a pro minent background population of CD68-positive dendritic cells. Ultrastructu ral studies showed that the tumour cells contained an excess of rough endop lasmic reticulum, with some of the cisternae appearing dilated, and scallop ing of the cell surfaces, although no intracisternal tubules were identifie d. Conclusions: Although the histological pattern was most reminiscent of extr askeletal myxoid chondrosarcoma, the sensitivity of the stroma to pretreatm ent with hyaluronidase precluded the diagnosis. However, there were similar ities with the sarcomatoid component of malignant salivary grand-type mixed tumours of the lung and this tumour possibly represents a variant of a bro nchial gland tumour. Despite this uncertainty over origin, this pattern sho uld be recognized as part of the differential diagnosis of myxoid tumours i n the lung, as an apparently indolent type of malignant endobronchial neopl asm.