Table 1 Classification systems of pathological response to neoadjuvant breast cancer treatment

ypT ypN, same categories as for adjuvant setting

No evaluation of response;

No published data relating current edition definitions to survival outcomes

Class 1. No invasive carcinoma or DCIS, negative lymph nodes

Class 1 and 2 = pCR (DCIS allowed)

Class 2. DCIS in the breast, no invasive carcinoma, negative lymph nodes

Class 3. Invasive carcinoma with stromal alteration

Class 4. Few modifications of tumour appearance

Tumour:

T-A includes pCR and minimal residual disease

 T-A. Total or near total therapeutic effect

T-A versus other categories associated with survival outcomes

 T-B. >50 % therapeutic effect, but less than T-A

 T-C. <50 % therapeutic effect

 T-D. No therapeutic effect

Nodes:

 N-A. Evidence of therapeutic effect, no metastasis

 N-B. No nodal metastasis or therapeutic effect

 N-C. Evidence of therapeutic effect, but metastasis present

 N-D. Metastatic disease, no therapeutic effect

Grade 1. No reduction in overall cellularity

DCIS allowed for pCR

Grade 2. Minor loss of tumour cells (up to 30 %)

Does not include response in the lymph nodes

Grade 3. 30–90 % reduction in tumour cellularity

Association with survival outcomes

Grade 4. >90 % loss of tumour cellularity

Grade 5. No malignant cells identifiable; DCIS may be present

Breast:

DCIS allowed for pCR

 1. pCR: (1) no residual carcinoma or (2) no residual invasive tumour but DCIS present.

 2. Partial response: (1) minimal residual disease ( <10 % of tumour remaining) , (2) evidence of response with 10–50 % of tumour remaining or (3) >50 % of tumour cellularity remaining with some features of response present.

 3. No evidence of response to therapy.

Lymph nodes:

Practical approach which is easy to apply

 1. No evidence of metastasis or response.

No published data regarding association with survival outcomes

 2. Metastases not present but evidence of response.

 3. Metastasis present with evidence of response.

 4. Metastasis present with no evidence of response.

Combines tumour size in two dimensions, average residual cellularity, number of involved nodes and size of largest metastases. Online calculator to generate a continuous numerical index that is subdivided into four classes (0 = pCR, I, II and III).

Quantifies residual disease rather than evaluates response

Reproducible and relatively easy to apply

Validated in several independent cohorts

Significant association with survival outcomes over long term follow up