Table 2.

Prognostic tumour type groups

Prognostic groups	Types
Very indolent (excellent prognosis similar to locally infiltrative lesions with limited metastatic potential)	Pure low‐grade adenosquamous carcinoma, pure fibromatosis like metaplastic carcinoma, pure low‐grade mucoepidermoid, adenoid cystic and secretory carcinomas 81 , * Other special type tumours which include encapsulated and solid papillary carcinomas that lack myoepithelial cells but staged as in situ disease (pTis), and other lesions such as atypical adenomyoepithelioma and malignant adenomyoepithelioma in situ. 82
Excellent prognosis group (low metastatic potential. Mainly lymph node metastasis)	Pure tubular and invasive cribriform carcinoma of limited size (<3 cm)*
Good prognosis group	Grade 1 invasive lobular, mucinous, invasive papillary and IBC‐NST, and tubulolobular carcinoma.
Moderate prognosis group	Grade 2 IBC‐NST, and invasive lobular carcinoma classical type.
Poor prognosis group	High grade IBC‐NST, solid and other high‐grade invasive lobular carcinoma, high‐grade matrix producing and squamous cell metaplastic carcinomas.
Very poor prognosis group	High grade spindle cell metaplastic carcinoma, small cell carcinoma and high‐grade triple‐negative IBC‐NST of large size.

^*These tumours should be small (<3 cm). During tumourigenesis, the cancer cells undergo replication and mutation, thereby increasing the tumour size is often associated with increasing invasiveness of the tumour. ⁸³ Larger size tumours are likely to have different tumour components and the behaviour is likely to relate to the other (more aggressive) carcinoma component. The basaloid and solid variant of adenoid cystic carcinoma is more aggressive. Also, some secretory carcinomas in older patients may behave less indolently.