When brain fragments from 10 day old brat¹⁸/brat¹⁴ mutant larvae are transplanted into adult hosts and incubated for 10 days the cells proliferate extensively and fill the host abdomen. brat¹⁸/brat¹⁴ tumours are able to pass through the muscle layer and form micrometastases. Cells are also able to pass through the basement membranes that surround the muscle layer of epithelial sheath, indicating that the tumour cells are able to completely pass through all three layers of the epithelial sheath. Each micrometastasis develops in the haemolymph filled space between the epithelial sheath and the basement membrane surrounding the follicular epithelium.

When transplanted into wild-type, brat¹⁸/brat¹⁴ tumor cells form micrometastases in 15% of ovarioles after 10 days of proliferation. brat¹⁸/brat¹⁴ brain fragments transplanted into ovo^D1 hosts for 7 days then wild-type hosts for 10 days form micrometastases in 20.5% of the ovarioles examined. This is not considered a significant increase. brat¹⁸/brat¹⁴ tissue serially transplanted in ovo^D1 hosts for two 7 day periods then into wild-type hosts for 10 days form micrometastases in 20% of the ovarioles examined (i.e. not a significant change with extended passaging). brat¹⁸/brat¹⁴ tumor cells that are grown in multiple hosts do not show any change in depth of penetration into the ovariole. All of the micrometastases exhibit a similar size and are found between the epithelial sheath and the follicular epithelium.

The brains of hemizygous third instar larvae are enlarged compared to wild-type. This is largely due to excessive growth in the posterior part of the brain in the region where the optic lobes develop.