Small cell carcinoma of unknown origin?

As far as I can tell reading here, http://mesothelioma-malignant.com/ , it could be, but probably not. Undifferentiated implies primitive and fundamentally different cells from the host body, which...

All living things are made up of cells. Because they are small in size does not mean that their cell size is small. Generally cells are the same size between organisms.

A bacteria cell is a prokaryotic cell, so no

No, all multicellular organisms have the same size cells.

Because the men that live inside them are only teeny tiny, so why would they need a large cell? Their mushroom houses just don't need the space