In this variety the alveoli are large and of various sizes and shapes, and are supported by a delicate stroma rich in blood-vessels. By mutual compression the cells assume different forms, and it may only be the deepest layer that presents the typical columnar shape, while it is often impossible to distinguish some parts of the section from the spheroidal-celled variety. Colloid degeneration is more frequent in this form than in the others (fig. 22).

Colloid carcinoma presents a fine meshwork of connective tissue, which encloses a large quantity of clear muco-colloid material. No cellular elements may exist, or here and there a few cells or fragments may be detected. At the margin of the tumour the usual appearances of carcinoma are to be found; and the process of degeneration may be traced in the development of clear globules in the substance of the cells, which gradually coalesce and destroy the regularity of their outline.