ECP 2023 Abstracts

S165 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 E-PS-02-049 A semiquantitative study of neuroendocrine differentiation on the breast cancer subtypes Y. Otsuki*, S. Ohtsuka, Y. Asano, T. Ikeya, Y. Ishida, S. Sezaki, H. Kobayashi *Seirei Hamamatsu General Hospital, Japan Background & objectives: Although breast cancers have been some- times reported to show neuroendocrine differentiation, few reports have examined percentage of the positive cells in the tumour with neuroen- docrine markers. We performed a semiquantitative study of neuroen- docrine differentiation on the tumour subtypes. Methods: Immunostaining for Synaptophysin, Chromogranin A, and INSM1 was performed on the pathological specimens. Their expression rates in the tumour cells were measured in a semiquantitative manner with three tiers of phenotypic expression on immunohistochemistry with the markers: diffuse-positive (>50% of tumour cells), focal-posi- tive (10-50%), and weak or negative (<10%). Results: The breast cancer subtype in this study included 127 cases of solid papillary carcinoma (SPC), 52 conventional ductal carcinoma in situ (DCIS), 41 invasive breast cancer of no special type (IBC-NST), 16 mucinous carcinoma (MUC) and 15 invasive lobular carcinoma (ILC). Number of the cases with diffuse positivity with at least one or more markers was 123 cases of SPC, 1 DCIS, 0 IBC-NST, 4 MUC, 0 ILC. And the number with focal positivity with at least one marker was 4 SPC, 5 DCIS, 1 IBC-NST, 5 MUC and 2 ILC. Weak or negative for all the markers were 0 SPC, 46 DCIS, 40 IBC-NST, 7 MUC, and 13 ILC. Conclusion: According to our result, the phenotypic expression of SPC quite differs from those of the other subtypes. SPC typically displays diffuse neuroendocrine differentiation, IBC-NST, conventional DCIS, and ILC rarely indicate obvious neuroendocrine differentiation. It is suggested that the immunohistochemistry will help us differentiate SPC from the other subtypes of the breast tumour. And SPC may be catego- rized into NET because of the clear neuroendocrine differentiation that sharply contrasts with the other subtype of the breast tumours. E-PS-02-050 Breast prognostic markers – three-year institutional experience and comparison with published benchmarks D. Proca*, Y. Belogrivtseva, I. Mazur *Temple University Health System, USA Background & objectives: College of American Pathologists rec- ommends that “for HER2 immunohistochemical (IHC) and in situ hybridization (ISH) and ER IHC tests performed on breast carcinoma that provide independent predictive information, the laboratory at least annually compares its patient results with published benchmarks.” Methods: We selected from the electronic data base all breast biop- sies and lumpectomies processed between Jan 2020 and January 2023 and looked at the prognostic marker results for all breast malignant tumours. Our institution performs ER, PR, and Her-2/ Neu testing on initial biopsy or lumpectomy, and only repeats the testing on the final resection specimen, for any negative marker. Results: 1134 total breast biopsies, lumpectomies, mastectomies were examined between 2020-2023 out of which: - 265 were invasive ductal carcinomas - 30 invasive lobular carcinoma - 3 LCIS - 93 DCIS - 5 medullary carcinoma - 5 mucinous carcinoma - 53 of 305 invasive carcinomas were triple negative, corresponding to 17.37% of invasive carcinoma cases; 2/53 were medullary carci- noma, 51/53 high grade invasive ductal carcinoma - 11/ 93 DCIS were ER negative )11.82%) - 33/ 265 invasive ductal carcinomas were Her-2/ Neu positive by immunohistochemistry or FISH (12.45%) - 21/ 265 ductal carcinoma had FISH performed (7.92%) for Her-2/ Neu 2/3 -1/ 30 lobular carcinomas (3.33%) was Her-2/ Neu positive. Conclusion: It is important for each laboratory to monitor the results of breast prognostic marker testing and compare them with published benchmarks as part of quality assurance plan. Published benchmarks are: ER-negative breast cancers (invasive and DCIS) should not exceed 30%. The proportion is somewhat lower in post vs premenopausal women (20% vs. 35%). ER-negative % is lower in well-differentiated carcinomas (<10%) and lobular, tubular, and mucinous carcinomas. For HER2 studies, the overall proportion of HER2 positive breast can- cers is 10-25%. E-PS-02-051 Primary neuroendocrine tumour of breast: a case report of a rare neoplasm I. Provatas*, P. Pantoula, D. Mylonaki, S. Efthymiou, A. Karakosta *Pathology Laboratory, General Hospital of Nikaia - Piraeus "Ag. Panteleimon", Greece Background & objectives: Breast Neuroendocrine Tumours (NETs) are uncommon, primary neuroendocrine neoplasm of the breast, requir- ing > 90% NET pattern, and neuroendocrine markers helpful for diag- nosis. They account < 1% of primary breast cancers, occurring most commonly to women elder than 65 years. Methods: We report a 89-year old female patient who was operated for a tumour in the left breast, following the diagnosis of NET in FNB specimen and the received mastectomy specimen measured 7x5x3 cm. On gross examination and serial sectioning, a whitish, circumscribed, solid, elastic tumour 1,7 cm was revealed, 1,7 cm in maximum diam- eter. Surgical margins were clear. Results: Microscopic study of tumour showed diffuse parenchymal infil- trates from a neoplasmwith a compact and atypically insular or cribriform growth pattern, composed of cells with mild cellular and nuclear atypia and polymorphism, eosinophilia and occasional granular cytoplasm, and low mitotic activity (~ 2 mitoses / 10 HPF). The immunohistochemical control of these cells revealed positivity for GATA-3, CD56, Synaptophy- sin and Chromogranin. In addition, global strong ER and PgR immuno- expression was observed, with negative Her2/Neu (1+). SSTR2a score was 2+ based on Volante et al scoring system and Ki-67 index was low, ranging at ~5%. Given the extent of the infiltrates, a diagnosis of well- differentiated neuroendocrine breast tumour was made. Conclusion: Neuroendocrine tumours are a group of rare breast neo- plasms. Their prognosis seems to depend on the number of mitoses and the Ki-67 index. Currently, there are no specific guidelines for their treatment, and they are graded based on existing criteria for other types of invasive breast carcinoma. Furthermore, they should not be confused with other breast neoplasms with neuroendocrine differentiation, such as mucinous type 2 carcinoma, solid papillary carcinoma, or ductal carcinoma with neuroendocrine differentiation. E-PS-02-053 Core needle biopsy diagnosis of fibroepithelial lesions of the breast and the upgrade rate in the surgical specimen: experience of an oncology hospital S. Reis*, N. Castelo-Branco, P. Figueiredo *Instituto Português de Oncologia, Portugal Background & objectives: Fibroepithelial lesions of the breast are a heterogenous group of biphasic tumours that share histological character- istics but can have a variable clinical behaviour. The aim is to study the concordance between core needle biopsy and surgical specimen diagnosis.