For ER+ breast cancers that are clinical Stage IIB (T2N1) nearing locally advanced stages, what criteria do you use to determine if you would offer neoadjuvant chemotherapy?

This is an interesting question. Assuming this is regarding ER positive but HER2 negative tumors, the factors I would consider that would favor the decision to use upfront chemotherapy are the following:

1. Tumors that are grade 3 or high Ki-67

2. Low ER positive tumors

3. Younger, premenopausal women, particularly if they desire breast conserving surgery

4. IDC vs ILC

5. Site of breast mass, if reduction in size would help surgical decisions

In general, if I believe that a patient would likely require chemo based on biology, I would consider upfront chemo.

I agree with the eloquent answer from @Dr. First Last.

I do exercise caution in doing Neo-adjuvant chemotherapy for ER positive, Her 2 Negative ( Luminal A) cancer outside of T3/4 or N2/3 disease.

Need for chemotherapy in ER positive T2N1 disease can't be ascertained without genomic assays.  

We do have predictive/prognostic data for pN1 disease, on both Oncotype Dx (Retrospective SWOG data and Prospective German phase 3 PlanB data) showing excellent outcome with endocrine therapy alone for those low risk patients. Mammaprint also have prospective data for pN1 disease. We also await results of completed RxPONDER study using Oncotype Dx for N1 disease. 

We also have published data supporting use of both Mammaprint and Oncotype on Core Bx, to guide us on neoadjuvant endocrine therapy versus chemotherapy, but there are certainly concerns on such testing on core tissue. 

Neo-adjuvant endocrine therapy should be a consideration in post-menopausal patients where need for chemotherapy is not certain. 

Two randomized phase II trials of neoadjuvant endocrine therapy vs. chemotherapy,  showed a similar response and rate of breast conservation for both treatment arms with substantially less toxicity with endocrine treatment :

1. Alba E, Calvo L, Albanell J, De la Haba JR, Arcusa Lanza A, Chacon JI, et al. Chemotherapy (CT) and hormonotherapy (HT) as neoadjuvant treatment in luminal breast cancer patients: results from the GEICAM/2006-03, a multicenter, randomized, phase-II study. Ann Oncol. 2012;23:3069–74.

2. Semiglazov VF, Semiglazov VV, Dashyan GA, Ziltsova EK, Ivanov VG, Bozhok AA, et al. Phase 2 randomized trial of primary endocrine therapy versus chemotherapy in postmenopausal patients with estrogen receptor-positive breast cancer. Cancer. 2007;110:244–54.

There is an interesting trial using neoadjuvant Recurrence Score and assessment of Ki67, ADAPT HR+/HER2– (NCT01779206) trial . In this trial, patients at diagnosis are assigned a risk category based on the Oncotype DX recurrence score (RS) and nodal status. A high risk group (N2-3, RS >26) received neoadjuvant chemotherapy. A low risk group (N0-1, RS ≤11) received NET alone or surgery followed by adjuvant endocrine therapy. Patients with intermediate risk cancers (N0-1, RS 12–25) received endocrine therapy for 2 weeks; those with a 2-week Ki67 ≤10% stayed on endocrine therapy to complete 3 months, while patients with Ki67 >10% were switched to chemotherapy.

if Her-2 NEU positive would definitely do neoadjuvant therapy , as if residual disease at end of neoadjuvant would be eligible for futher anti her-2 neu therapy