Table 1 Comparison of features between the constitutive MMTV-PyV mT/MMTV-Cre recombinase model and the inducible MMTV-rtTA/TetO-MIC model

PyV mT transgene promoter

Mouse mammary tumour virus (MMTV)

Tetracycline operator (TetO)

Inducible transgene expression

No

Yes

Coupling to Cre recombinase

No

Yes

Time when 50% of animals have tumours (T ₅₀ )

40 days of age [6]

7 days of induction

Tumour pathology

Solid adenocarcinoma [3, 4]

Solid adenocarcinoma

Cre recombinase expression and function in PyV mT tumour cells (by X-gal assay)

0% when conditional gene is essential for tumourigenesis [5–7]

100%

Percentage of tumour-bearing mice with lung metastases

93.3% [6]

100%