Correlation of in vitro cell viability and cumulative singlet oxygen luminescence from protoporphyrin IX in mitochondria and plasma membrane.

SIGNIFICANCE: Photodynamic therapy (PDT) can be targeted toward different subcellular localizations, and it is proposed that different subcellular targets vary in their sensitivity to photobiological damage. Since singlet oxygen (1O2) has a very short lifetime with a limited diffusion length in cellular environments, measurement of cumulative 1O2 luminescence is the most direct approach to compare the PDT sensitivity of mitochondria and plasma membrane. APPROACH: PDT-generated near-infrared 1O2 luminescence at 1270 nm was measured together with cell viability for 5-aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) and exogenous PpIX, at different incubation times. Confocal fluorescence microscopy indicated that ALA-induced PpIX (2 h) localized in the mitochondria, whereas exogenous PpIX (1 h) mainly localized to the plasma membrane. Cell viability was determined at several time points during PDT treatments using colony-forming assays, and the surviving fraction correlated well with cumulative 1O2 luminescence counts from PpIX in mitochondria and plasmas membrane, respectively. RESULTS: The mitochondria are more sensitive than the plasma membrane by a factor of 1.7. CONCLUSIONS: Direct 1O2 luminescence dosimetry's potential value for comparing the PDT sensitivity of different subcellular organelles was demonstrated. This could be useful for developing subcellular targeted novel photosensitizers to enhance PDT efficiency.

Updated retinoblastoma incidence and outcome in children in Taiwan from 1980 to 2019: a 40-year nationwide study.

BACKGROUND: Retinoblastoma is a potentially fatal disease, and its incidence and mortality varies among different countries and periods. METHODS: This is a nationwide population-based retrospective study from January 1980 to December 2019 in Taiwan. Patients diagnosed as retinoblastoma were identified from the Taiwan National Cancer Registry. To update the literature on retinoblastoma incidence, mortality and trends in Taiwan, we analysed changes in incidence and survival rates over time according to sex, diagnostic age, laterality and treatment. RESULTS: During 1980-2019, the incidence of retinoblastoma in Taiwan was 1 per 16 489 live births (95% CI: 13 415-19 564). The diagnostic age decreased from 2.21 ± 0.26 during 1980-1984 to 1.24 ± 0.26 during 1985-2019. Compared with that observed during 1980-1989, the incidence rate observed after 1990 increased significantly in children aged <10 years (RR: 1.62-2.40, P = 0.0049 to < 0.0001). From 1980 to 2019, the incidence rate for the 0-4-year age group increased and that for the 5-9-year age group remained constant. The mean diagnostic age for bilateral retinoblastoma (0.36 ± 0.47 years) was significantly less than that for unilateral retinoblastoma (1.37 ± 0.35 years) during 2007-2019 (P < 0.0001). The 10-year survival rate was highest in the enucleation group (89.8%) compared with radiotherapy (52.2%) and others (70.0%; P < 0.0001). CONCLUSIONS: During 1980-2019 in Taiwan, the incidence of retinoblastoma increased significantly, and the diagnostic age decreased, which are similar to the ones from other developed countries. However, the survival rate was still lower than that of most developed countries.

Inhibition of Heat Shock-Induced H3K9ac Reduction Sensitizes Cancer Cells to Hyperthermia.

Heat stress, clinically known as hyperthermia, is a promising adjunctive modality in cancer treatment. However, the efficacy of hyperthermia as a monotherapy is limited and the underlying mechanism remains poorly understood. Targeting histone modifications is an emerging strategy for cancer therapy, but little is known regarding the role of heat stress in altering these modifications. Here, we report that heat shock inhibits H3K9 acetylation (H3K9ac) via histone deacetylase 6 (HDAC6) regulation. Heat shock inhibits the interaction between HDAC6 and heat shock protein 90 (HSP90), enhances nuclear localization of HDAC6, and promotes HDAC6 phosphorylation, which is regulated by protein phosphatase 2A (PP2A). Combining hyperthermia with HDAC inhibitors vorinostat or panobinostat leads to better anti-cancer effects compared to monotherapy. KEAP1 and DPP7 as genes affected by heat-induced inhibition of H3K9ac, and combining them with hyperthermia can better induce apoptosis in tumor cells. This study reveals previously unknown mechanisms of H3K9ac decreased by heat shock in cancer cells and highlights a potential combinational therapy involving hyperthermia and targeting of these new mechanisms.

Novel chlorin e6-based conjugates of tyrosine kinase inhibitors: Synthesis and photobiological evaluation as potent photosensitizers for photodynamic therapy.

Since tyrosine kinase inhibitor (TKI) could reverse ABCG2-mediated drug-resistance, novel chlorin e6-based conjugates of Dasatinib and Imatinib as photosensitizer (PS) were designed and synthesized. The results demonstrated that conjugate 10b showed strongest phototoxicity against HepG2 and B16-F10 cells, which was more phototoxic than chlorin e6 and Talaporfin. It could reduce efflux of intracellular PS by inhibiting ABCG2 in HepG2 cells, and localize in mitochondria, lysosomes, golgi and ER, resulting in higher cell apoptosis rate and ROS production than Talaporfin. Moreover, it could induce cell autophagy and block cell cycle in S phase, and significantly inhibit tumor growth and prolong survival time on BALB/c nude mice bearing HepG2 xenograft tumor to a greater extent than chlorin e6. Consequently, compound 10b could be applied as a promising candidate PS due to its good water-solubility and stability, low drug-resistance, high quantum yield of 1O2 and excellent antitumor efficacy in vitro and in vivo.

Revisiting the Graphitized Nanodiamond-Mediated Activation of Peroxymonosulfate: Singlet Oxygenation versus Electron Transfer.

Graphitized nanodiamonds (ND) exhibit outstanding capability in activating peroxymonosulfate (PMS) for the removal of aqueous organic micropollutants (OMPs). However, controversial observation and interpretation regarding the effect of graphitization degree on ND's activity and the role of singlet oxygen (1O2) in OMP degradation need to be clarified. Herein, we investigated graphitized ND-mediated PMS activation. Experiments show that the activity of ND increases first and then decreases with the monotonically increased graphitization degree. Further experimental and theoretical studies unveil that the intensified surface graphitization alters the degradation mechanism from singlet oxygenation to an electron-transfer pathway. Moreover, for the first time, we applied a self-constructed, time-resolved phosphorescence detection system to provide direct evidence for 1O2 production in the PMS-based system. This work not only elucidates the graphitization degree-dependent activation mechanism of PMS but also provides a reliable detection system for in situ analysis of 1O2 in future studies.

Quenching effects of (-)-Epigallocatechin gallate for singlet oxygen production and its protection against oxidative damage induced by Ce6-mediated photodynamic therapy in vitro.

BACKGROUND: Singlet oxygen (1O2) is highly reactive to biological components such as lipids, proteins and DNA, which induces oxidative damage to cells and tissues. Natural antioxidants may function as 1O2 quencher to prevent 1O2 involved photosensitized oxidation in biological system. METHODS: Time-resolved measurement of 1O2 luminescence was employed to evaluate the 1O2 quenching abilities of natural antioxidants in air-statured phosphate buffered saline (PBS), including (-)-Epigallocatechin gallate (EGCG), Proanthocyanidins, L-carnosine and Vitamin C. The 1O2 quenching effects and rate constant of EGCG were investigated by detecting the absorption, fluorescence and 1H-NMR spectroscopy and 1O2 luminescence decay curves, respectively. In addition, the protective activity of EGCG against 1O2 oxidative damage caused by Ce6-mediated photodynamic therapy (PDT) was verified in cells. RESULTS: EGCG, proanthocyanidins, L-carnosine and Vitamin C efficiently quenched 1O2 luminescence at 1270 nm. The triplet-state quenching rate constants of EGCG for Rose Bengal (RB), Chlorin e6, AlPcS and HiPorfin are 2.21 × 109, 4.90 × 108, 3.30 × 108, 1.78 × 109 M-1s-1, while the 1O2 quenching rate constants are 2.80 × 108, 1.50 × 108, 1.30 × 108, 1.70 × 108 M-1s-1, respectively. Furthermore, EGCG could effectively quench 1O2 production to prevent NIH/3T3 cells oxidative damage induced by Ce6-mediated PDT. CONCLUSIONS: EGCG is an efficient quencher for both triplet-state photosensitizers and 1O2. The quenching ability of EGCG during photosensitization for selected photosensitizers is: RB > HiPorfin > Ce6 > AlPcS. EGCG could be used to protect normal cells and tissue against oxidative damage.

Singlet Oxygen Luminescence Image in Blood Vessels During Vascular-Targeted Photodynamic Therapy.

Singlet oxygen (1 O2 ) is widely regarded as the main cytotoxic substance that induces the biological damage for photodynamic therapy (PDT). In this study, the previously developed near-infrared (NIR) optical imaging system was optimized for fast imaging of 1 O2 luminescence. The optical imaging system enables direct imaging of 1 O2 luminescence in blood vessels within 2 s during vascular-targeted PDT (V-PDT), which makes this system extremely practical for in vivo studies. The dependence of RB concentration on 1 O2 luminescence image was investigated for V-PDT, and the data imply that 1270 nm signal is attributed to 1 O2 luminescence. The imaging system operates with a field of view of 9.60 × 7.68 mm2 and a spatial resolution of 30 µm, which holds the potential to elucidate the correlation between cumulative 1 O2 luminescence and vasoconstriction for V-PDT.

Discovery of atorvastatin as a tetramer stabilizer of nuclear receptor RXRα through structure-based virtual screening.

Retinoid X receptor alpha (RXRα), a central member of the nuclear receptor superfamily and a key regulator of many signal transduction pathways, has been an attractive drug target. We previously discovered that an N-terminally truncated form of RXRα can be induced by specific ligands to form homotetramers, which, as a result of conformational selection, forms the basis for inhibiting the nongenomic activation of RXRα. Here, we report the identification and characterization of atorvastatin as a new RXRα tetramer stabilizer by using structure-based virtual screening and demonstrate that virtual library screening can be used to aid in identifying RXRα ligands that can induce its tetramerization. In this study, docking was applied to screen the FDA-approved small molecule drugs in the DrugBank 4.0 collection. Two compounds were selected and purchased for testing. We showed that the selected atorvastatin could bind to RXRα to promote RXRα-LBD tetramerization. We also showed that atorvastatin possessed RXRα-dependent apoptotic effects. In addition, we used a chemical approach to aid in the studies of the binding mode of atorvastatin.

Design, synthesis and biological evaluation of tetrazole-containing RXRα ligands as anticancer agents.

Nuclear receptor RXRα plays an important role in many biological and pathological processes. The nongenomic action of RXRα is implicated in many cancers. K-8008, a non-canonical RXRα ligand derived from sulindac, inhibits the TNFα-activated PI3K/AKT pathway by mediating the interaction between a truncated form of RXRα (tRXRα) and the p85α regulatory subunit of PI3K and exerts potent anticancer activity in animal model. Herein we report our studies of a novel series of K-8008 analogs as potential anticancer agents targeting RXRα. Two compounds 8b and 18a were identified to have slightly stronger binding to RXRα and improved apoptotic activities in breast cancer cells.

Maps of in vivo oxygen pressure with submillimetre resolution and nanomolar sensitivity enabled by Cherenkov-excited luminescence scanned imaging.

Low signal-to-noise ratios and limited imaging depths restrict the ability of optical-imaging modalities to detect and accurately quantify molecular emissions from tissue. Here, by using a scanning external X-ray beam from a clinical linear accelerator to induce Cherenkov excitation of luminescence in tissue, we demonstrate in vivo mapping of the oxygenation of tumours at depths of several millimetres, with submillimetre resolution and nanomolar sensitivity. This was achieved by scanning thin sheets of the X-ray beam orthogonally to the emission-detection plane, and by detecting the signal via a time-gated CCD camera synchronized to the radiation pulse. We also show with experiments using phantoms and with simulations that the performance of Cherenkov-excited luminescence scanned imaging (CELSI) is limited by beam size, scan geometry, probe concentration, radiation dose and tissue depth. CELSI might provide the highest sensitivity and resolution in the optical imaging of molecular tracers in vivo.

Cherenkov-excited Multi-Fluorophore Sensing in Tissue-Simulating Phantoms and In Vivo from External Beam Radiotherapy.

In this work, Cherenkov-excited molecular sensing was used to assess the potential for simultaneous quantitative sensing of two NIR fluorophores within tissue-simulating phantoms through spectral separation of signals. Cherenkov emissions induced by external beam gamma photon radiation treatment to tissues/tissue-simulating phantoms were detectable over the 500-900-nm wavelength range. The presence of blood was demonstrated to reduce the integrated intensity of detected Cherenkov emissions by nearly 50%, predominantly at wavelengths below 620 nm. The molecular dyes, IRDye 680RD and IRDye 800CW, have excitation and emission spectra at longer wavelengths than the strongest blood absorption peaks, and also where the intensity of Cherenkov light is at its lowest, so that the emission signal relative to background signal is maximized. Tissue phantoms composed of 1% intralipid and 1% blood were used to simulate human breast tissue, and vials containing fluorophore were embedded in the media, and irradiated with gamma photons for Cherenkov excitation. We observed that fluorescence emissions excited by the Cherenkov signal produced within the phantom could be detected at 5-mm depth into the media within a 0.1-25 µ M fluorophore concentration range. The detected fluorescence signals from these dyes showed linear relationships with radiation doses down to the cGy level. In vivo tests were successful only within the range near a µ M, suggesting that these could be used for metabolic probes in vivo where the local concentrations are near this range.

OCT imaging detection of brain blood vessels in mouse, based on semiconducting polymer nanoparticles.

Optical Coherence Tomography (OCT) is a valuable technology that has been used to obtain microstructure images of tissue, and has several advantages, though its applications are limited in high-scattering tissues. Therefore, semiconducting polymer nanoparticles (SPNs) that possess strong absorption characteristics are applied to decrease light scattering in tissues and used as exogenous contrast agents for enhancing the contrast of OCT imaging detection. In this paper, we prepared two kinds of SPNs, termed PIDT-TBZ SPNs and PBDT-TBZ SPNs, as the contrast agents for OCT detection to enhance the signal. Firstly, we proved that they were good contrast agents for OCT imaging in agar-TiO2. After that, the contrast effects of these two SPNs were quantitatively analyzed, and then cerebral blood vessels were monitored by a home-made SD-OCT system. Finally, we created OCT images in vitro and in vivo with these two probes and performed quantitative analysis using the images. The results indicated that these SPNs created a clear contrast enhancement of small vessels in the OCT imaging process, which provides a basis for the application of SPNs as contrast agents for bioimaging studies.

Review of fluorescence guided surgery systems: identification of key performance capabilities beyond indocyanine green imaging.

There is growing interest in using fluorescence imaging instruments to guide surgery, and the leading options for open-field imaging are reviewed here. While the clinical fluorescence-guided surgery (FGS) field has been focused predominantly on indocyanine green (ICG) imaging, there is accelerated development of more specific molecular tracers. These agents should help advance new indications for which FGS presents a paradigm shift in how molecular information is provided for resection decisions. There has been a steady growth in commercially marketed FGS systems, each with their own differentiated performance characteristics and specifications. A set of desirable criteria is presented to guide the evaluation of instruments, including: (i) real-time overlay of white-light and fluorescence images, (ii) operation within ambient room lighting, (iii) nanomolar-level sensitivity, (iv) quantitative capabilities, (v) simultaneous multiple fluorophore imaging, and (vi) ergonomic utility for open surgery. In this review, United States Food and Drug Administration 510(k) cleared commercial systems and some leading premarket FGS research systems were evaluated to illustrate the continual increase in this performance feature base. Generally, the systems designed for ICG-only imaging have sufficient sensitivity to ICG, but a fraction of the other desired features listed above, with both lower sensitivity and dynamic range. In comparison, the emerging research systems targeted for use with molecular agents have unique capabilities that will be essential for successful clinical imaging studies with low-concentration agents or where superior rejection of ambient light is needed. There is no perfect imaging system, but the feature differences among them are important differentiators in their utility, as outlined in the data and tables here.

Light sheet luminescence imaging with Cherenkov excitation in thick scattering media.

Light scattering leads to a severe loss of axial and transverse resolution with depth into tissue, limiting accuracy and value of biomedical luminescence imaging techniques. High-resolution imaging beyond a few-millimeter depth is prohibited because diffusive transport dominates beyond a few scattering distances. In this study, light sheet imaging through scattering media is demonstrated using a radiotherapy linear accelerator to deliver well-defined thin scanned sheets of x-rays. These sheets produce Cherenkov light within the medium, which in turn excites luminescence of an optical probe across the sheet plane. This luminescence can then be imaged by an intensified camera positioned perpendicular to the sheet plane. The precise knowledge of the light sheet position within the medium allowed for efficient attenuation correction of the signal with depth as well as spatial deconvolution of the excitation light. Together these methods allowed for the first time, to the best of our knowledge, high-resolution imaging of tissue-equivalent phantoms up to 3 cm thick, yielding the precise position and shape of luminescent lesions located deep in tissue without the need for nonlinear image reconstruction.

Photosensitized singlet oxygen generation and detection: Recent advances and future perspectives in cancer photodynamic therapy.

Photodynamic therapy (PDT) uses photosensitizers and visible light in combination with molecular oxygen to produce reactive oxygen species (ROS) that kill malignant cells by apoptosis and/or necrosis, shut down the tumor microvasculature and stimulate the host immune system. The excited singlet state of oxygen (1 O2 ) is recognized to be the main cytotoxic ROS generated during PDT for the majority of photosensitizers used clinically and for many investigational new agents, so that maximizing its production within tumor cells and tissues can improve the therapeutic response, and several emerging and novel approaches for this are summarized. Quantitative techniques for 1 O2 production measurement during photosensitization are also of immense importance of value for both preclinical research and future clinical practice. In this review, emerging strategies for enhanced photosensitized 1 O2 generation are introduced, while recent advances in direct detection and imaging of 1 O2 luminescence are summarized. In addition, the correlation between cumulative 1 O2 luminescence and PDT efficiency will be highlighted. Meanwhile, the validation of 1 O2 luminescence dosimetry for PDT application is also considered. This review concludes with a discussion on future demands of 1 O2 luminescence detection for PDT dosimetry, with particular emphasis on clinical translation. Eye-catching color image for graphical abstract.

Comparison of Cherenkov excited fluorescence and phosphorescence molecular sensing from tissue with external beam irradiation.

Ionizing radiation delivered by a medical linear accelerator (LINAC) generates Cherenkov emission within the treated tissue. A fraction of this light, in the 600-900 nm wavelength region, propagates through centimeters of tissue and can be used to excite optical probes in vivo, enabling molecular sensing of tissue analytes. The success of isolating the emission signal from this Cherenkov excitation background is dependent on key factors such as: (i) the Stokes shift of the probe spectra; (ii) the excited state lifetime; (iii) the probe concentration; (iv) the depth below the tissue surface; and (v) the radiation dose used. Previous studies have exclusively focused on imaging phosphorescent dyes, rather than fluorescent dyes. However there are only a few biologically important phosphorescent dyes and yet in comparison there are thousands of biologically relevant fluorescent dyes. So in this study the focus was a study of efficacy of Cherenkov-excited luminescence using fluorescent commercial near-infrared probes, IRDye 680RD, IRDye 700DX, and IRDye 800CW, and comparing them to the well characterized phosphorescent probe Oxyphor PtG4, an oxygen sensitive dye. Each probe was excited by Cherenkov light from a 6 MV external radiation beam, and measured in continuous wave or time-gated modes. The detection was performed by spectrally resolving the luminescence signals, and measuring them with spectrometer-based separation on an ICCD detector. The results demonstrate that IRDye 700DX and PtG4 allowed for the maximal signal to noise ratio. In the case of the phosphorescent probe, PtG4, with emission decays on the microsecond (µs) time scale, time-gated acquisition was possible, and it allowed for higher efficacy in terms of the probe concentration and detection depth. Phantoms containing the probe at 5 mm depth could be detected at concentrations down to the nanoMolar range, and at depths into the tissue simulating phantom near 3 cm. In vivo studies showed that 5 nmol of dye was readily detected with radiation doses less than 5 cGy. Since concentration, radiation dose and depth each contribute to the level of the detected signal, it may be possible to improve any of these parameters at expense of the others. This paradigm of nanoMolar sensitivity for optical reporters in vivo introduces the concept of molecular sensing of tumors during therapy or diagnostically with biologically relevant concentrations of fluorescent reporters.

Logarithmic intensity compression in fluorescence guided surgery applications.

The use of fluorescence video imaging to guide surgery is rapidly expanding, and improvements in camera readout dynamic range have not matched display capabilities. Logarithmic intensity compression is a fast, single-step mapping technique that can map the useable dynamic range of high-bit fluorescence images onto the typical 8-bit display and potentially be a variable dynamic contrast enhancement tool. We demonstrate a ∼4.6 times improvement in image quality quantified by image entropy and a dynamic range reduction by a factor of ∼380 by the use of log-compression tools in processing in vivo fluorescence images.

A novel chlorin-PEG-folate conjugate with higher water solubility, lower cytotoxicity, better tumor targeting and photodynamic activity.

Techniques to enhance tumor targeting and to improve the aqueous solubility of anticancer drugs and photosensitizers have recently been the focus of much research. In this study, a folate-PEG-conjugated chlorin was synthesized and characterized. Because of the use of PEG as a linker, the new chlorin displayed increased aqueous solubility, with a solubility of 40.1mg/mL in PBS, and showed lower aggregation and cytotoxicity than its precursor, chlorin. Meanwhile, the introduction of folic acid to the new chlorin resulted in increased selectivity for folate-receptor-positive tumor cells (HeLa and Hep-2 cells); the cellular uptake of the new chlorin by HeLa and Hep-2 cells was strikingly higher than that of the precursor chlorin, and the photocytotoxicities of the new chlorin to HeLa and Hep-2 cells were 2.5 and 3.5 times greater than that of folate-free conjugate chlorin. During photodynamic therapy mediated by the new chlorin, both type I and type II reactions occur simultaneously.

Feasibility study on quantitative measurements of singlet oxygen generation using singlet oxygen sensor green.

The purpose of this study is to investigate the feasibility for quantitative measurement of singlet oxygen ((1)O(2)) generation by using a newly developed (1)O(2)-specific fluorescence probe Singlet Oxygen Sensor Green reagent (SOSG). (1)O(2) generation from photoirradiation of a model photosensitizer Rose Bengal (RB), in initially air-statured phosphate buffered saline (PBS) was indirectly monitored with SOSG. In the presence of (1)O(2), SOSG can react with (1)O(2) to produce SOSG endoperoxides (SOSG-EP) that emit strong green fluorescence with the maximum at 531 nm. The green fluorescence of SOSG-EP is mainly dependent on the initial concentrations of RB and SOSG, and the photoirradiation time for (1)O(2) generation. Furthermore, kinetic analysis of the RB-sensitized photooxidation of SOSG is performed that, for the first time, allows quantitative measurement of (1)O(2) generation directly from the determination of reaction rate. In addition, the obtained (1)O(2) quantum yield of porphyrin-based photosensitizer hematoporphyrin monomethyl ether (HMME) in PBS by using SOSG is in good agreement with the value that independently determined by using direct measurement of (1)O(2) luminescence. The results of this study clearly demonstrate that the quantitative measurement of (1)O(2) generation using SOSG can be achieved by determining the reaction rate with an appropriate measurement protocol.

[Clinicopathologic features of micropapillary variant of pure mucinous carcinoma of breast].

OBJECTIVE: To study the clinicopathologic features of pure mucinous carcinomas of the breast with diffuse micropapillary pattern. METHODS: Twenty-six cases of micropapillary variant of pure mucinous carcinoma of the breast were retrospectively reviewed by light microscopy, immunohistochemistry and clinical data analyses. RESULTS: The age of 26 female patients ranged from 30 to 77 years old, of which 12 cases with clinical details available were mean 54 years old. The tumor diameter ranged from 0.8 to 9.0 cm (mean 3.2 cm). Ipsilateral axillary nodal metastases were identified in 3 cases. Cutaneous involvement was also found in 2 cases. The tumor cells showed the similar architectural arrangement as in invasive micropapillary carcinoma, with peripheral borders of the cell clusters highlighted by epithelial membrane antigen. Various amount of mucin occupied the retraction spaces around the tumor cells. Compared with conventional pure mucinous carcinoma of the breast, mucinous carcinomas with micropapillary pattern showed different nuclear grades (19 cases of grade I, 2 cases of grade II, 5 cases of grade III). The micropapillary cell clusters varied in size (22 cases of big micropapillary and 4 cases of small). Intraductal carcinoma was observed in 12 cases. Calcification and psammoma bodies were observed in 8 cases. Immunophenotyping, the tumor cells were with higher expression of hormone receptors, but HER2 were negative. Ki-67 positive index was 1% ∼ 70%. Neuroendocrine differentiation was observed in 6 cases. CONCLUSIONS: The micropapillary variant of pure mucinous carcinoma of the breast, which mainly occurs in younger women, may carry the similar propensity for angioinvasion and nodal metastasis as infiltrating micropapillary carcinoma at least in cases with high nuclear grade. This morphologic subtype needs to be distinguished from conventional pure mucinous carcinoma of the breast and treated properly.