Citations

e17610 Background: Methylated DNA markers (MDMs) associated with sporadic ovarian cancer (OC) are detected in plasma from patients with treatment naïve tumors, but not cancer-free controls. To assess potential benefits to patients at risk for hereditary OC, the aim of this study was to measure the performance of validated sporadic OC MDMs in OC and benign ovarian tissue (BOT), surgically obtained from germline BRCA1 or BRCA2 ( BRCA1/2) mutation carriers. Methods: BRCA1/2 carriers with OC and BRCA1/2 carriers who had undergone risk-reducing salpingo-oophorectomy (SO) were identified at a comprehensive cancer center. BRCA1/2 carriers in both OC and BOT groups were balanced on age and year of surgery with non- BRCA carriers with sporadic OC or benign indications for SO. OC and BOT formalin fixed paraffin embedded (FFPE) tissues were macrodissected following pathologist selection of representative sites; DNA was extracted, and bisulfite converted. 15 OC MDMs ( GDF6, IFFO1, MAX.chr1.147790358, MAX.chr6.10382190, MAX.chr11.14926602, C2CD4D, PDRM14, NCOR2, SKI, DSCR6, SIM2, PALLD, CDO1, GPRIN1, BCAT1) previously identified in sporadic OC were assayed by quantitative methylation specific PCR, normalized by β-actin, by blinded personnel. Areas under the receiver operating characteristic curve (AUC) were generated for each MDM to assess discrimination of OC from benign tissue and compared between BRCA1/2 and sporadic (non- BRCA) patients, using a z-test. Results: Among BRCA1/2 carriers, there were 48 OC ( BRCA-OC) and 48 BOT ( BRCA-BOT); among non- BRCA, we matched 48 OC (Sporadic-OC) and 48 BOT (non- BRCA-BOT). The median AUC for OC MDM discriminated between OC and BOT with AUCs in BRCA1/2 carriers was 0.87, (IQR, 0.83-0.93). Sporadic-OC vs non- BRCA-BOT median AUC was 0.88 (IQR, 0.83-0.92). AUCs were not significantly different for each MDM when stratified by BRCA or sporadic status. MDMs with an AUC of ≥0.9 in either group are shown (Table). Conclusions: OC MDMs identified and validated in sporadic OC are highly discriminant for OC from BOT in DNA extracted from tissues of people who carry a BRCA1/2 mutation. Testing the performance of these OC MDMs in plasma from BRCA1/2 carriers with and without OC may be of clinical value for high-risk patients and inform multi-cancer early detection testing strategies.[Table: see text]

555 Background: Women with early-stage breast cancer (BCa) are living longer, and survivorship issues including second primary cancers (SPCs) are therefore increasingly important. This study seeks to determine the risk of SPCs, including contralateral breast cancer (CBCa), in women with early-stage invasive lobular carcinoma (ILC). Methods: The study population consisted of women with BCa diagnosis between 2000-2018 within the NCI Surveillance, Epidemiology, and End Results (SEER v 3.2.9) registry and between 2000-2021 in the Mayo Clinic Cancer Registry. In the SEER registry, the standardized incidence ratios (SIR) for SPCs were estimated for adult women with histologically confirmed early stage (I-III) ILC compared to the development of any primary cancer in the general population. For reference, SIRs for SPCs for a similar patient population with invasive ductal carcinoma (IDC) of the breast were also estimated. For comparison of CBCa between ILC and IDC, follow up records from the Mayo Clinic Cancer Registry were evaluated among adult women who underwent lumpectomy or unilateral mastectomy for early stage ILC or IDC. A multivariable Cox proportional hazards regression was performed to compare the risk of CBCa between ILC and IDC while adjusting for the age at diagnosis, race/ethnicity and estrogen receptor status of the primary tumor. Results: An increased incidence (p<0.05) of any SPCs and second BCa was noted for both ILC and IDC compared to the expected rate of primary cancer in the general population (Table). Interestingly, women with ILC were observed to have a significantly increased incidence of subsequent gastric cancer which was not seen for women with IDC. An SIR >1.5 was noted for subsequent risk of sarcoma, myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) for both ILC and IDC (Table). In the Mayo Clinic Cancer Registry of 2,218 women with ILC and 14,629 women with IDC meeting the inclusion criteria, the 5-year risk of CBCa was 2.6% and 1.5% (log rank statistic p-value =0.001) for ILC and IDC respectively. A significantly increased risk of CBCa was noted in women with ILC (Hazard Ratio 1.82, 95% CI 1.34-2.47, p<0.001) compared to women with IDC in the multivariable analysis. Conclusions: Women with ILC may have an increased risk of SPC and second BCa compared to the risk of any primary cancer in the general population. The increased incidence of gastric cancer and the higher risk of CBCa in ILC survivors compared to women with IDC is intriguing and needs to be investigated further including evaluation of the role of germline genetic factors. [Table: see text]

Abstract Background: The lack of consensus on whether bilateral oophorectomy impacts risk of developing breast cancer among BRCA1 mutation carriers might be attributed to various biases, specifically, cancer-induced testing bias due to inclusion of prevalent cases. We conducted two complementary matched case–control analyses to evaluate the association of oophorectomy and BRCA1 breast cancer. Methods: A research questionnaire was administered every two years to collect information on exposures and disease. In the first analysis, we limited the study to prevalent breast cancer cases (diagnosed prior to study entry; n = 2,962) who were matched to controls on year of birth and country of residence (n = 4,358). In the second approach, we limited to 330 incident cases (diagnosed in the follow-up period) and 1,548 matched controls. Conditional logistic regression was used to estimate the adjusted odds ratios (OR) and 95% confidence intervals (CI) of invasive breast cancer. Results: In the first approach, there was a significant inverse association between oophorectomy and the risk of developing breast cancer [OR = 0.43; 95% confidence interval (CI), 0.34–0.55; P &lt; 00001]. In the second approach, there was no association between oophorectomy and risk (OR = 1.21; 95% CI, 0.87–1.70; P = 0.26). Conclusions: The inclusion of women with a personal history of breast cancer prior to ascertainment likely impacts upon the association of oophorectomy and BRCA1 breast cancer risk. Impact: Oophorectomy is unlikely a determinant of breast cancer risk in BRCA1 mutation carriers but should be offered at age 35 to reduce the risk of ovarian and fallopian tube cancer.

Abstract Background: Hormone receptor-positive (HR+) breast cancer (BC) accounts for ~60-70% of all BC cases. CDK4/6i combined with endocrine therapy (ET) is the standard of care for first- and second-line therapy of patients with HR+ metastatic breast cancer (MBC) based on substantial improvements in progression free survival (PFS) and overall survival compared to ET alone. Unfortunately, most patients (pts) develop resistance to CDK4/6i. The mechanisms underlying CDK4/6i resistance have not been fully elucidated. Robust in vivo CDK4/6i resistant animal models from pts with de novo and acquired CDK 4/6i resistance are lacking. Patient-derived xenografts (PDXs) are important preclinical tools in oncology to advance our understanding of cancer biology and to evaluate drug response phenotypes. Unfortunately, the establishment of sustainable PDXs from pts with HR+ BC is much more difficult than from HR-negative BC. In order to obtain clinically relevant models that can be utilized to better understand mechanisms of primary and acquired resistance to ET and CDK4/6i, we report the development of PDXs from a prospective study in which percutaneous biopsies were obtained from women receiving palbociclib for the treatment of HR+ advanced or MBC (PROMISE; NCT03281902). Methods: PROMISE (Prospective Study to Evaluate the Role of Tumor Sequencing in Women Receiving Palbociclib for Advanced Hormone Receptor (HR)-Positive Breast Cancer) is a prospective trial which enrolled pts with HR+, HER2-negative MBC who planned to start treatment with palbociclib and letrozole (1st line [FL]) or palbociclib and fulvestrant (2nd line [SL]). For pts enrolled at Mayo Clinic Rochester (MCR), serial tumor biopsies were obtained prior to the start of treatment and at disease progression to establish PDXs. Because baseline take rate was low, we amended the protocol to attempt PDX generation after the 2nd cycle (C2) of therapy. Tissues were received within an hour of excision and were orthotopically implanted in the mammary fat pad of 6~8-week-old nonobese diabetic (NOD)/SCID/IL-2g-receptor null (NSG) mice. Tumor growth was defined as tumor volume ≥ 50 mm3. Tumor take rate was defined as percent of patients with development of at least one stably transplantable (passed at least for two generations) xenograft that was pathologically confirmed as BC. Results: Of the 50 pts enrolled at MCR, 37 were FL pts (2 ineligible) and 13 were SL pts (1 ineligible). Fresh tumor samples obtained pre-treatment from 43 eligible pts (32 FL), after C2 from 17 eligible pts (13 FL), and at disease progression from 10 eligible pts (5 FL) were implanted. Tumor growth was seen in at least one mouse from a pre-treatment specimen in 1 (3.1%) FL pt (confirmed BC) and 4 (36.4%) SL pts (2 confirmed BC); from end of C2 specimens in 2 (15.4%) FL pts and 2 (50%) SL pts (1 confirmed BC); and at progression in 1 (20%) FL pt and 2 (40%) SL pts (1 confirmed BC). The take rate from pre-treatment samples among FL pts was 1/32 (3.1%; 95% CI: 0.08-16.2%). Take rates in other groups are pending histological review. Discussion: In pts receiving palbociclib for HR+ MBC, the take rate using a pre-treatment percutaneous biopsy was low (3.1%) in the FL setting. However, higher growth rates were seen in the SL setting. The observation of higher growth rates at the end of C2 and at progression may relate to the activation of G1/S that occurs with withdrawal of palbociclib, and should be further studied. PDX remains a valuable tool for the evaluation of tumor biology and the development of new therapeutics, especially for those models established from pts with palbociclib and ET resistance. Proteogenomic and sequencing studies are ongoing to fully characterize these PDXs. Citation Format: Jia Yu, Vera J. Suman, Jun He, Jason P. Sinnwell, Ann M. Moyer, Bo Qin, Yayun Gu, Huan Zhang, Jodi M. Carter, Krishna R. Kalari, Brendan P. McMenomy, Minetta C. Liu, Tufia C. Haddad, Kathryn J. Ruddy, Fergus J. Couch, Alvaro Moreno-Aspitia, Donald W. Northfelt, Richard Weinshilboum, Ciara O'Sullivan, Matthew P. Goetz, Liewei Wang. Patient-derived xenografts (PDXs) generated from hormone receptor-positive breast cancer (BC) before and after cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) treatment: Initial findings from the PROMISE study [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-01-07.

Abstract Introduction: Breast cancer treatments can impair fertility via direct gonadotoxicity (chemotherapy) as well as by introducing delays in childbearing that allow natural ovarian aging. Guidelines strongly recommend fertility counseling and consideration of fertility preservation techniques for premenopausal women who have not completed their desired childbearing at the time of cancer diagnosis. Prior studies have identified high rates of fertility concern but relatively low rates of fertility counseling and use of fertility preservation techniques. We sought to investigate rates of fertility counseling, use of fertility preservation techniques, and how fertility concerns impact cancer treatment decisions in a modern cohort of patients with breast cancer at a large academic medical center in the United States. Methods: All patients seen at Mayo Clinic Rochester with a new diagnosis (within the year prior) of stage 0-4 breast cancer were invited (by mail or in person) to participate in the Mayo Clinic Breast Registry. After informed consent, participants were asked to complete a baseline survey and annual follow-up surveys. On baseline and one-year surveys, patients were queried about desire for future children and fertility concerns. Nurse chart abstraction was used to collect information about tumor subtype, stage, and treatments received. We examined survey data from women diagnosed under the age of 50 who expressed an interest in having future biological children on either the baseline or year 1 survey between February 2015 and October 2020. Descriptive statistics were used to summarize the degree of fertility concern in this population, the impact of that concern on cancer treatment decisions, and steps taken to preserve fertility. Results: Between February 2015 and October 2020, 865 women under age 50 at diagnosis consented to the registry. Of these women, 627 completed a baseline and/or 1-year survey and 100 answered either “yes” or “unsure” to the question: “At the present time, do you wish to have any more biological children in the future?” on one or both surveys. Among the 100 women expressing interest in future child-bearing, 92% were white, 27% had node-positive and one had distant metastatic disease at diagnosis. The age at diagnosis ranged from 19 to 49 years, with a mean age of 33.8 years. Of the 75 who reported a desire for future children at baseline, 28% felt “somewhat concerned” about their future fertility and 40% felt “very concerned.” Of the 70 who reported a desire for future children on the year 1 survey, 17% felt “somewhat concerned” and 59% felt “very concerned.” For those “very concerned” about future fertility at year 1, 65% reported that this concern had a major impact on their treatment decisions. Often, that treatment modification entailed using endocrine therapy for less than 5 years; 52% of those who specified the type of treatment modification they had made indicated this option. Of note, six women who reported no desire for future biological children at baseline were “unsure” at year 1. At year 1, 93% of women recalled a discussion about fertility with their doctor prior to starting treatment, and 49% had taken steps to preserve fertility (32.5% with embryo cryopreservation, 20% with oocyte cryopreservation and 65% with a GnRH agonist; some selected multiple options). Conclusion: We found a reassuringly high rate of patient-reported fertility counseling and use of reproductive endocrinology technologies to preserve fertility in women who reported a desire for additional children at or soon after diagnosis with breast cancer. Consistent with prior studies, fertility concerns frequently impacted breast cancer treatment decisions. It is important to err on the side of inclusivity when providing fertility counseling because desire for fertility can change over time. Citation Format: Samantha Mannion, Alexandra Higgins, Elizabeth A Stewart, Zaraq Khan, Chandra Shenoy, Nicole Larson, Hazel B Nichols, H Irene Su, Ann H Partridge, Fergus J Couch, Janet E Olson, Kathryn Ruddy. Prevalence and impact of fertility concerns in young women with breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P4-11-02.

Abstract Funding Source: Institutional funds at Mayo Clinic. Background: While alopecia is a common and distressing acute side effect of chemotherapy, chronic hair thinning is also reported by some survivors during endocrine therapy. The purpose of the current study was to evaluate real world experiences of late/long-term alopecia among breast cancer survivors. Methods: Breast cancer survivors participating in the ongoing prospective Mayo Clinic Breast Disease Registry (MCBDR) were mailed a survey six years after diagnosis, between June and November 2020. Respondents were asked to report how bothered they are by hair thinning and hair loss over the last year on a scale from 0 “not at all” to 4 “extremely”. They were also asked whether they used any hair thickening or regrowth products. Results: 552/899 survivors responded (response rate 61%); 403 survivors’ responses were available for analysis. Respondents’ median age was 66 years, and median time since diagnosis was 78 months. Seventy patients (17%) were diagnosed with stage 0 breast cancer, 195 (48%) were diagnosed with stage 1 cancer, 104 (26%) with stage 2, 25 (6%) with stage 3; 6 (1%) had been diagnosed with metastatic or recurrent disease at the time of this survey. 139 (34%) patients had received chemotherapy. Of the patients who received chemotherapy, 82 (59%) had received doxorubicin and cyclophosphamide, 41 (29%) received docetaxel and cyclophosphamide, 77 (55%) received paclitaxel, and 27 (19%) received carboplatin. 258 (64%) received endocrine therapy. Of these patients who received endocrine therapy, 131 (51%) received Tamoxifen and 186 (72%) received aromatase inhibitors. 309 survivors (77%) were 55 years or older. 189 (47%) of all patients reported that they were bothered by chronic hair loss, and 225 (56%) reported that they were bothered by hair thinning; 71 (18%) reported use of thickening/regrowth products. There did not appear to be differences in chronic hair loss or thinning by receipt of chemotherapy: 64 patients (46%) who received chemotherapy reported hair loss and 79 (56%) reported hair thinning, compared with 123 patients (46%) who did not receive chemotherapy and reported hair loss and 142 (54%) who reported hair thinning. Hair thinning or loss did not appear to differ based upon age (Table 1). Symptoms did not appear to be more common amongst current or previous endocrine therapy recipients, with 113 (44%) of that subset bothered by hair loss and 128 (50%) by hair thinning. Conclusion: Hair loss and thinning are frequently reported as bothersome symptoms by long-term breast cancer survivors. Future investigations into treatments for chronic hair thinning during and after cancer therapy are needed. Table 1.&lt; 5555+Bothered by hair loss (n)%Bothered by hair thinning (n)%Bothered by hair loss (n)%Bothered by hair thinning (n)%Not at all5761%4649%15751%13142%Slightly1920%2426%8728%9731%Moderately77%910%3110%4113%BOTHERED BY HAIR LOSS (N)%BOTHERED BY HAIR THINNING (N)%BOTHERED BY HAIR LOSS (N)%BOTHERED BY HAIR THINNING (N)%Quite a bit77%1112%227%268%Extremely44%33%93%103%Missing00%11%31%41% Citation Format: Elizabeth Cathcart-Rake, Charles L Loprinzi, Janet E Olson, Fergus Couch, Brittany Dulmage, Maryam Lustberg, Nicole Larson, Kathryn J Ruddy. Alopecia among breast cancer survivors [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P4-10-17.

Abstract Background: Eyebrow and eyelash loss are widely recognized as consequences of some chemotherapies, but prevalence and predictors are understudied. The purpose of this study was to evaluate real world experiences of eyebrow and eyelash loss during treatment for breast cancer. Methods: Breast cancer survivors participating in the ongoing prospective Mayo Clinic Breast Disease Registry (MCBDR) were mailed a survey one year after diagnosis. Respondents were asked to recall their severity of eyebrow and eyelash loss since diagnosis, measured from “no loss” to “a little loss” to “a lot of loss” to “complete loss”. Results: 524 participants were mailed a survey including these questions between May 2020 and November 2020; the median time from diagnosis to survey completion was 12 months (range 6 months). Of the 265 participants whose responses were available for analysis (median age 60.8 years), 88 (33%) had received chemotherapy, including 39 (44%) who received doxorubicin and cyclophosphamide, 16 (18%) who received docetaxel and cyclophosphamide, 56 (64%) who received paclitaxel, and 11 (13%) who received carboplatin. 173 (65%) had received endocrine therapy: 56 (32%) of patients who received endocrine therapy received tamoxifen, and 115 (66%) received aromatase inhibitors. 124 (47%) reported at least a little eyebrow loss, and 22 (8%) reported complete loss. Forty-seven percent reported at least a little eyelash loss, and 27 (10%) reported complete loss (Table 1). In the subgroup of 88 patients who received chemotherapy, the rates of at least a little eyebrow and eyelash loss were 50% and 55%, respectively, and rates of complete loss were 8% and 9%. Rates of eyebrow and eyelash loss did not appear to differ significantly by age. Conclusion: Eyebrow and eyelash loss are frequently reported during breast cancer-directed therapy. Future investigations into the incidence and treatment of this side effect are needed. Table 1.&lt;55 years old55+ years oldEyebrow Loss (N)%Eyelash Loss (N)%Eyebrow Loss (N)%Eyelash Loss (N)%No Loss4551%4753%9655%9353%A Little Loss2629%2225%3922%3922%A lot of loss1011%1112%2715%2514%Complete Loss89%910%148%1810%Funding Source: Breast Cancer Research Foundation (CLL) Clinic Citation Format: Elizabeth Cathcart-Rake, Charles L Loprinzi, Fergus Couch, Janet Olson, Brittany Dulmage, Maryam Lustberg, Nicole Larson, Kathryn J Ruddy. Eyebrow/eyelash loss among survivors [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P4-10-11.

Abstract Introduction: The risk of specific clinical subtype of breast cancer (defined by ER and HER2 status) among women in the general population who are carriers of germline pathogenic variants (PVs) in cancer predisposition genes is not well-defined. Methods: A total of 13,153 women with breast cancer (ER+/HER2-: 9381; ER+/HER2+: 1462; ER-/HER2+: 690; and ER-/HER2-: 1620) and 25,005 unaffected women (controls) from nine studies within the CAnceR RIsk Estimates Related to Susceptibility (CARRIERS) consortium that were not enriched for family history or early onset disease were included in the present analysis. A multiplex amplicon-based panel was used to perform germline sequencing for cancer predisposition genes. Case-control associations for each of the four clinical subtype of breast cancer was performed for PVs in 5 common breast cancer predisposition genes (ATM, BRCA1, BRCA2, CHEK2 and PALB2) utilizing a logistic regression model adjusting for study, age at diagnosis, race/ethnicity and family history of breast cancer. Results: The frequency of PVs in 5 genes was 3.8% for ER+/HER2-, 6.2% for ER+/HER2+, 4.2% for ER-/HER2+ and 9.3% for ER-/HER2- subtypes. PVs in BRCA1 and BRCA2 were associated with high risk (Odds Ratio (OR) &gt;4) for all clinical subtypes of breast cancer, but the risk was highest (OR&gt;8) for ER-/HER2- breast cancer. PVs in PALB2 were associated with high risk (OR&gt;4) of ER-/HER2- and ER+/HER2+ subtypes and moderate risk (OR: 2-4) of ER+/HER2- breast cancer. Irrespective of the HER2 status, PVs in ATM were associated with a moderately increased risk (OR: 2-4) of ER+ breast cancer but the risk of ER- breast cancer was not elevated. In contrast, PVs in CHEK2 were associated with high risk (OR&gt;4) of ER+/HER2+ breast cancer and moderate risk (OR: 2-4) of ER+/HER2- and ER-/HER2+ breast cancer, but the risk of ER-/HER2- breast cancer was not elevated. Conclusions: This study provides population-based estimates of risk of specific clinical subtypes of breast cancer which will be useful for genetic counseling and targeting appropriate screening strategies in PV carriers based on subtype specific risks of breast cancer. Citation Format: Siddhartha Yadav, Chunling Hu, Nicholas J. Boddicker, Eric Polley, Steven Hart, Rohan Gnanaolivu, Jie Na, Hongyan Huang, Song Yao, Celine M. Vachon, Lauren Teras, Jack A. Taylor, Dale P. Sandler, Julie R. Palmer, Janet E. Olson, Susan Neuhausen, Elena Martinez, Sara Lindstroem, Loic Le Marchand, Charles Kooperberg, Christopher Haiman, Mia M. Gaudet, James V. Lacey, Kimberly A. Bertrand, Leslie Bernstein, Paul W. Auer, Christine Ambrosone, Jeffrey N. Weitzel, Peter Kraft, David E. Goldgar, Katherine L. Nathanson, Susan M. Domchek, Fergus J. Couch, CARRIERS Consortium. Population-based risk estimates of clinical subtypes of breast cancer among carriers of germline pathogenic variants in cancer predisposition genes [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-09-01.

Abstract Background: The importance of the antitumor immune response in TNBC is well established. TNBC with higher TILs are less likely to recur and more responsive to systemic therapy. Likewise, PD-L1+ TNBC are more likely to benefit from chemoimmunotherapy. However, TNBC is highly heterogeneous. Of the TNBC molecular subtypes, LAR TNBC is less sensitive to systemic therapy, has lower TILs and lower rates of PD-L1 positivity. The role of other immune related proteins in LAR TNBC is not well established. Here, we evaluated differentially expressed (DE) immune related proteins in the stromal and intratumoral compartments of LAR vs non-LAR TNBC tumors. Methods: We used the Nanostring GeoMX DSP platform to quantitate 58 proteins within spatially distinct intraepithelial, cytokeratin (CK)-positive tumor segments and adjacent CK-negative/nuclei-positive stromal segments in 248 TNBC tumors included in a tissue microarray generated from a cohort of pts with centrally confirmed TNBC who underwent breast surgery without prior neoadjuvant therapy. A subset (n=111) underwent bulk tumor RNA sequencing and were classified as LAR or non-LAR TNBC. DE proteins were identified using a negative binomial generalized linear model (SNR&gt;2, p&lt;0.05). A targeted set of DE proteins was dichotomized at the 80th percentile. Results: Of 111 TNBC tumors, 17 (15%) were LAR and 94 (85%) non-LAR. Compared to non-LAR TNBC, pts with LAR TNBC were older (age ≥50: 82% vs 52%, p&lt;0.01), with tumors that were more often of apocrine histology (35% vs 0%, p &lt;0.01), grade 1-2 (24% vs 1%, p&lt;0.01), and had lower Ki67 (Ki67 ≤15: 24% vs 11%, p=0.06). Most tumors were T1-2 (94% vs 93%, p=0.82) and N0 (53% vs 62%, p=0.09), respectively. As expected, expression of most immune-related proteins was higher in the stromal vs the intratumoral compartment for both LAR and non-LAR TNBC. When focusing on the stromal compartment, expression of multiple immune related proteins was significantly lower in LAR compared to non-LAR TNBC, including the pan-leukocyte marker CD45 (log-2 fold change [log2FC]: 0.552, p=0.05), the macrophage marker CD14 (log2FC: 0.834, p=0.06), CD44 (lof2FC: 0.637, p=0.07), and the immune checkpoint proteins IDO1 (log2FC: 0.914, p=0.04), VISTA (log2FC: 0.471, p=0.07), ICOS (log2FC: 0.444, p=0.08), and STING (log2FC: 0.544, p=0.09). Proteins with expression levels too low for comparisons included PD-L1, LAG3, FOXP3 and BCL-2. When focusing on the intratumoral compartment, expression of most immune-related proteins was very low in both LAR and non-LAR TNBC. Like in the stromal compartment, CD45 expression was lower in LAR TNBC (log2FC: 0.78, p=0.02). Expression of the immune checkpoint B7-H3 was lower in LAR TNBC (log2FC: 0.737, p=0.02), while expression of the T cell marker CD127 was higher (log2FC: -0.528, p=0.34). With regards to relevant non-immune markers, expression of Ki67 was lower in LAR TNBC (log2FC: 0.5498, p=0.05), consistent with the clinical assay. Conclusion: In this ultra high-plex spatial analysis, we provide first insights into the differential expression at the protein level of several targetable immune checkpoint molecules in LAR vs non-LAR TNBC. The lower expression of several immune related proteins in LAR TNBC is consistent with the hypothesis that LAR TNBC exhibits a “cold” immune microenvironment compared to other TNBC subtypes, potentially rendering itself less susceptible to immunotherapy-based strategies. These data support the need to consider TNBC molecular subtypes in future evaluations of immune-based therapeutic approaches. Funding: This work was supported by NIH grant P50CA116201 to RLF, JMC, KRK, FJC, DZ, JNI, and MPG; BCRF grant 19-161 to EAT and NCATS grant CTSA KL2 TR002379 to RLF. The contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIH Citation Format: Roberto A Leon-Ferre, Jodi M. Carter, David M. Zahrieh, David W. Hillman, Saranya Chumsri, Yaohua Ma, Jennifer M. Kachergus, Xue Wang, Judy C. Boughey, Minetta C. Liu, James N. Ingle, Krishna R. Kalari, Jose C. Villasboas Bisneto, Fergus J. Couch, E. Aubrey Thompson, Matthew P. Goetz. Digital spatial profiling of immune-related proteins in luminal androgen receptor (LAR) vs non-LAR triple-negative breast cancer (TNBC) [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-04-01.