A Simple Method to Avoid Bile Duct Injury during Percutaneous Radiofrequency Ablation Therapy for Hepatocellular Carcinoma.

Hepatocellular carcinoma represents a major global health burden. Its treatment is often complicated by the anatomical location of tumors, which can lead to adverse outcomes. Radiofrequency ablation has recently gained attention as a safe method for treating hepatocellular carcinoma, but only in tumors that are not adjacent to bile ducts. Here, we report a new method for cooling the bile duct during radiofrequency ablation therapy, in which the outer jacket of an elastor needle was fixed and flash-cooled with chilled saline. This method was applied in a patient with hepatocellular carcinoma tumors near the main bile duct. The patient underwent successful radiofrequency ablation with bile duct cooling. The advantages of this method include low medical cost, simpler securing of nonexpanded bile ducts, and simultaneous removal upon termination of the radiofrequency ablation therapy. Bile duct complications associated with radiofrequency ablation typically have delayed onset. Computed tomography examination 2 months after treatment showed no bile duct injury in this case.

Procedure of Direct Hepatic Artery Puncture for the Treatment of Hepatocellular Carcinoma: Two Case Reports.

Recently, treatment options for hepatocellular carcinoma (HCC) have expanded due to the development of the tyrosine kinase inhibitor ramucirumab and immune checkpoint inhibitors. Transcatheter arterial chemoembolization is the standard therapy for intermediate-stage HCC; however, in cases with anatomical problems, normal approaches are not possible. In such rare cases, direct hepatic puncture may be considered as an effective therapy and an indispensable treatment. We report our novel method of direct hepatic artery puncture in this case report. In 2011 and 2017, we reported 2 cases in the journal of the Japan Society of Hepatology in Japanese. This therapy is difficult and is associated with a high risk of complications; however, we succeeded in both cases in a similar way. We believe this method may provide an alternative treatment when standard treatment is not possible or when urgent therapy is required. In case 1, direct hepatic artery puncture was performed under ultrasonographic guidance, and we were able to control the disease with percutaneous lipiodol chemotherapy. Case 2 was an emergency case of ruptured HCC. Direct hepatic puncture successfully stopped tumor bleeding; furthermore, tumor necrosis also occurred, as seen on the enhanced computed tomography image. Our new method requires advanced puncture techniques and is not the treatment of choice if there are other safe alternatives available. However, it can be considered as an option if there are no other viable, effective treatments.

Involvement of herbal medicine as a cause of mesenteric phlebosclerosis: results from a large-scale nationwide survey.

BACKGROUND: Mesenteric phlebosclerosis (MP) is a rare disease characterized by venous calcification extending from the colonic wall to the mesentery, with chronic ischemic changes from venous return impairment in the intestine. It is an idiopathic disease, but increasing attention has been paid to the potential involvement of herbal medicine, or Kampo, in its etiology. Until now, there were scattered case reports, but no large-scale studies have been conducted to unravel the clinical characteristics and etiology of the disease. METHODS: A nationwide survey was conducted using questionnaires to assess possible etiology (particularly the involvement of herbal medicine), clinical manifestations, disease course, and treatment of MP. RESULTS: Data from 222 patients were collected. Among the 169 patients (76.1 %), whose history of herbal medicine was obtained, 147 (87.0 %) used herbal medicines. The use of herbal medicines containing sanshishi (gardenia fruit, Gardenia jasminoides Ellis) was reported in 119 out of 147 patients (81.0 %). Therefore, the use of herbal medicine containing sanshishi was confirmed in 70.4 % of 169 patients whose history of herbal medicine was obtained. The duration of sanshishi use ranged from 3 to 51 years (mean 13.6 years). Patients who discontinued sanshishi showed a better outcome compared with those who continued it. CONCLUSIONS: The use of herbal medicine containing sanshishi is associated with the etiology of MP. Although it may not be the causative factor, it is necessary for gastroenterologists to be aware of the potential risk of herbal medicine containing sanshishi for the development of MP.

Validity of new methods to evaluate renal function in cancer patients treated with cisplatin.

PURPOSE: Creatinine clearance (Ccr) is used as a marker of renal function in cancer chemotherapy, but it is not correlated with glomerular filtration rate (GFR) after high-dose cisplatin treatment. In addition to Ccr, measured using 24-h urine collection (24-h Ccr) or Cockcroft-Gault formula (CGF), the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation and the Japanese GFR estimation equation (the Japanese equation) have been recently developed to estimate GFR for predicting renal function. However, these equations remain to be evaluated, particularly in cancer patients treated with cisplatin. Therefore, we investigated the validity of these equations for predicting the GFR in cancer patients treated with cisplatin. METHODS: GFR was measured by inulin clearance (Cin) in 50 cancer patients and compared with GFR estimated by the CKD-EPI equation, the Japanese equation, and Ccr estimated by CGF or measured by 24-h Ccr before the first and third cisplatin-containing chemotherapy cycles (considered pretreatment and posttreatment, respectively). RESULTS: Before treatment, the CKD-EPI and the Japanese equations estimated GFR with higher accuracy than Ccr. Posttreatment bias values for GFR estimation using the CKD-EPI and the Japanese equations were lower than those for Ccr. The CKD-EPI and the Japanese equations were also more precise than Ccr. However, for patients with low renal function, these equations still overestimated Cin. CONCLUSION: The CKD-EPI and the Japanese equations estimated GFR with lower bias and higher precision than Ccr pre- and postcisplatin treatment. This study is registered at UMIN: 000002167.

Rhabdomyolysis Caused by Candida parapsilosis in a Patient with Acute Myeloid Leukemia after Bone Marrow Transplantation.

Rhabdomyolysis is characterized by a marked elevation of the creatine kinase (CK) levels and myoglobinuria, thus leading to renal dysfunction. Various viruses or bacteria can be etiologic agents, but mycosis has only rarely been reported to be a cause of rhabdomyolysis. In this report, we describe an adolescent male with acute myeloid leukemia who underwent allogeneic bone marrow transplantation and thereafter developed rhabdomyolysis and Candida parapsilosis fungemia almost at the same time. Following treatment for C. parapsilosis, the transaminase and CK levels both satisfactorily decreased. This case illustrates that C. parapsilosis infection may be a causative agent of rhabdomyolysis in immunocompromised patients.

TYRO3 as a potential therapeutic target in breast cancer.

AIM: We evaluated the potential of TYRO3 as a therapeutic target in various types of breast cancer cell lines. MATERIALS AND METHODS: The effects of TYRO3-knockdown by small interfering RNA (siRNA) on proliferation, cell-cycle distribution, and cell signaling in four estrogen receptor (ER)-positive/HER2-non-amplified (luminal-type), two ER-negative/HER2-amplified (HER2-type), and two ER-negative/HER2-non-amplified (triple negative [TN]-type) cell lines were compared. RESULTS: Whereas TYRO3 knockdown induced the greatest proliferation suppression in luminal-type cells, and to a lesser extent in HER2-type cells, no proliferation inhibition was observed in TN-type cells. The TYRO3 siRNA-induced proliferation inhibition in luminal-type cells was observed in both estradiol (E2)-rich and -null conditions. The proliferation suppression was correlated with G0-G1/S cell-cycle arrest. Western blot analysis showed a decrease in phosphorylation of ERK1/2 or STAT3, and in cyclin D1 only in cell lines sensitive to TYRO3-knockdown. CONCLUSION: TYRO3 is a potential therapeutic target in breast cancer, particularly in luminal-type cells.

Hypothyroidism in patients with colorectal carcinoma treated with fluoropyrimidines.

Targeted therapy with tyrosine kinase inhibitors, including vascular endothelial growth factor receptors, has been demonstrated to induce hypothyroidism and thyroid dysfunction. Cancer patients with thyroid dysfunction may be underdiagnosed and undertreated. Thyroid function in colorectal cancer patients receiving fluoropyrimidine-based chemotherapy with or without bevacizumab was evaluated at baseline and monthly. In the present study, 3 of 27 (11.1%) patients who received fluoropyrimidine-based chemotherapy developed a thyroid-stimulating hormone (TSH) level >10 µU/ml, and 13 (48.1%) developed an elevation above the upper limit of the normal range. No difference in TSH elevation was noted between the bevacizumab and chemotherapy-alone group (50 vs. 45%; P=1.00, respectively). Three (11.1%) patients developed a TSH level >10 µU/ml and 2 with hypothyroidism were treated with thyroid hormone replacement therapy. We demonstrated that bevacizumab does not affect thyroid function but fluoropyrimidines may induce thyroid dysfunction in patients with colorectal cancer. Further investigation is required to clarify the mechanism of fluoropyrimidine-induced thyroid dysfunction.

Excessive MET signaling causes acquired resistance and addiction to MET inhibitors in the MKN45 gastric cancer cell line.

The clinical efficacy of MET tyrosine kinase inhibitors (MET-TKIs) is hindered by the emergence of acquired resistance, presenting an obstacle to drug discovery. To clarify the mechanisms underlying acquired resistance to MET-TKIs, we established resistance models by continuous exposure of the MET-amplified gastric cancer cell line MKN45 to MET-TKIs, PHA665752 (MKN45-PR) and GSK1363089 (MKN45-GR). Baseline expression and phosphorylation of MET were elevated in MKN45-PR and MKN45-GR compared to MKN45 cells, and higher concentrations of MET-TKIs were required to inhibit MET phosphorylation compared to parental cells. Alterations in MET previously associated with resistance to MET-TKIs were observed in resistant cells, including elevated MET copy number, observed in both resistant lines compared to MKN45 cells, and the Y1230H mutation, detected in MKN45-PR cells. Notably, the growth of resistant lines was lower in the absence of MET-TKIs, suggesting "addiction" to inhibitors. While MKN45-PR cells exhibited a higher S-phase fraction in the absence of PHA665752, bromodeoxyuridine (BrdU) uptake was identical. Baseline phosphorylation of ATR, Chk1 and p53 and p21(waf1/Cip1) expression was higher in MKN45-PR compared to MKN45 cells, and levels were reduced to those observed in untreated MKN45 cells following PHA665752 treatment. Furthermore, targeted knockdown of MET enhanced the growth of MKN45-PR cells. These findings suggest that alterations in MET leading to acquired MET-TKI resistance, may cause excessive MET signaling, subsequent replication stress and DNA damage response, and intra-S-phase arrest in the absence of MET-TKIs. Thus, partial MET inhibition is necessary for resistant cells to proliferate, a phenomenon we refer to as MET-TKI "addiction".

Tolvaptan as an alternative treatment for refractory fluid retention associated with sinusoidal obstruction syndrome after allogeneic stem cell transplantation.

Tolvaptan is an oral vasopressin V2-receptor antagonist recognized as effective for fluid retention associated with congestive heart failure and liver cirrhosis. However, there have been no reports concerning clinical experience with tolvaptan for sinusoidal obstruction syndrome (SOS). A 42-year-old male with primarily refractory T-lymphoblastic lymphoma underwent allogeneic peripheral blood stem cell transplantation from an HLA-matched sibling donor. The myeloablative conditioning regimen consisted of busulfan and cyclophosphamide. On day 20, the total bilirubin level was elevated to 2.0 mg/dL, and body weight increased from 76 to 85 kg, allowing a diagnosis of SOS to be made. Treatments with thrombomodulin, furosemide, carperitide, and low-dose dopamine were ineffective. By day 27, the patient's body weight had increased to 90 kg, and he subsequently developed cardiopulmonary failure. Therefore, we administered low-dose tolvaptan for 2 days (3.75 mg on day 27 and 7.5 mg on day 28). Consequently, his ascites and edema were significantly reduced, and body weight returned to 77 kg by day 34. However, he died of lymphoma progression on day 55. Tolvaptan may be an alternative and promising treatment for refractory fluid retention associated with SOS, although it is unclear whether tolvaptan administration leads to improvement in clinical outcome.

Mechanisms of acquired resistance to insulin-like growth factor 1 receptor inhibitor in MCF-7 breast cancer cell line.

The purpose of this study was to clarify the mechanism of acquired resistance to the insulin-like growth factor-1 receptor (IGF-1R) tyrosine kinase inhibitor NVP-AEW541. We developed an acquired resistant model by continuously exposing MCF-7 breast cancer cells to NVP-AEW541 (MCF-7-NR). MCF-7 and MCF-7-NR were comparatively analyzed for cell signaling and cell growth. While phosphorylation of Akt was completely inhibited by 3 µM NVP-AEW541 in both MCF-7 and MCF-7-NR, phosphorylation of S6K remained high only in MCF-7-NR, suggesting a disconnection between Akt and S6K in MCF-7-NR. Consistently, the mTOR inhibitor everolimus inhibited phosphorylation of S6K and cell growth equally in both lines. Screening of both lines for phosphorylation of 42 receptor tyrosine kinases with and without NVP-AEW541 showed that Tyro3 phosphorylation remained high only in MCF-7-NR. Protein expression of Tyro3 was found to be higher in MCF-7-NR than in MCF-7. Gene silencing of Tyro3 using siRNA resulted in reduced cell growth and cyclin D1 expression in both lines. While Tyro3 expression was inhibited by NVP-AEW541 and everolimus in MCF-7, it was reduced only by everolimus in MCF-7-NR. These findings suggested that cyclin D1 expression was regulated in a S6K/Tyro3-dependent manner in both MCF-7 and MCF-7-NR, and that the disconnection between IGF-1R/Akt and S6K may enable MCF-7-NR to keep cyclin D1 high in the presence of NVP-AEW541. In summary, acquired resistance to NVP-AEW541 appears to result from IGF-1R/Akt-independent activation of S6K and expression of Tyro3 and cyclin D1.

Regulation of MET kinase inhibitor resistance by copy number of MET in gastric carcinoma cells.

We previously established acquired resistant models for MET-tyrosine kinase inhibitors (TKIs) by continuously exposing the MET-amplified gastric cancer cell line MKN45 to MET-TKIs, PHA665752 (MKN45-PR), or GSK1363089 (MKN45-GR). We found resistant mechanisms caused by increased copy number of MET in both lines and Y1230H mutation in MKN45-PR. We also found that excessive MET signaling caused by these MET alterations resulted in intra-S-phase arrest in the absence of MET-TKIs, so that cells grew faster in the presence of MET-TKIs, a phenomenon referred to as "addiction." In this study, to investigate reversibility of the acquired resistance and "addiction" to MET-TKIs and their causative MET alterations, we sequentially cultured MKN45-PR and MKN45-GR in decreasing concentrations of MET-TKIs until they were able to grow in a drug-free condition. These "revertant" cell lines (designated MKN45-PR-RE and MKN45-GR-RE) were comparatively analyzed. Growth assay showed that both MKN45-PR-RE and MKN45-GR-RE partially lost the property of "addiction" to MET-TKIs. MKN45-GR-RE lost the property of resistance to GSK1363089, but MKN45-PR-RE retained resistance to PHA665752. Copy numbers and expression and phosphorylation of MET protein reduced in both MKN45-PR-RE and MKN45-GR-RE compared with MKN45-PR and MKN45-GR, respectively, but Y1230H mutation and biochemical resistance to PHA665752 remained in MKN45-PR-RE. The "addiction" to MET-TKIs appeared attributable to increased copy number, and the property and the MET alteration were reversible. The Y1230H mutation appeared enough in itself to keep cells resistant to MET-TKIs and was irreversible.

Inhibition of the mTOR/S6K signal is necessary to enhance fluorouracil-induced apoptosis in gastric cancer cells with HER2 amplification.

The purpose of this study was to explore the effect of trastuzumab in enhancing the activity of chemotherapeutic agents and the molecular basis of this effect. Two gastric cancer cell types with HER2 amplification, one sensitive (NCI­N87) and one insensitive (MKN-7) to trastuzumab, were tested for the effects of trastuzumab on cell growth and cell signaling using MTS assay and western blotting, respectively. Interaction between trastuzumab and chemotherapeutic agents (fluorouracil, doxorubicin, cisplatin and paclitaxel) was evaluated by the combination index (CI). Fluorouracil-induced apoptosis was evaluated using western blot for poly (ADP-ribose) polymerase (PARP). Trastuzumab decreased phosphorylation of S6K, showed synergistic effect with fluorouracil or doxorubicin, and increased fluorouracil-induced apoptosis in NCI-N87 cells, but not in MKN-7 cells. While the mTOR inhibitor everolimus enhanced fluorouracil-induced apoptosis in both HER2-amplified cell lines, this was not the case in the gastric cancer cell lines without HER2 amplification. Consistently, while the EGFR/HER2 inhibitor Cl-387,785 inhibited cell growth of MKN-7, this growth inhibition did not accompany decrease in phosphorylation of S6K, and the compound did not enhance fluorouracil-induced apoptosis. In summary, inhibition of the mTOR/S6K signal may be a key molecular event in enhancing fluorouracil-induced apoptosis specifically in gastric cancer cells with HER2 amplification. mTOR inhibitors may therefore be attractive alternative drugs in gastric cancers with HER2 amplification regardless of their sensitivity to trastuzumab.

Foretinib (GSK1363089), a multi-kinase inhibitor of MET and VEGFRs, inhibits growth of gastric cancer cell lines by blocking inter-receptor tyrosine kinase networks.

To explore the mechanism of action of foretinib (GSK1363089), an oral multi-kinase inhibitor known to target MET, RON, AXL, and vascular endothelial growth factor receptors (VEGFRs), in gastric cancer, we evaluated the effects of the agent on cell growth and cell signaling in the following panel of gastric cancer cell lines: KATO-III, MKN-1, MKN-7, MKN-45, and MKN-74. Of these, only MKN-45 and KATO-III, which harbor MET and fibroblast growth factor receptor 2 (FGFR2) amplification, respectively, were highly sensitive to foretinib. In MKN-45, 1 µM of foretinib or PHA665752, another MET kinase inhibitor, inhibited phosphorylation of MET and downstream signaling molecules as expected. In KATO-III, however, PHA665752 inhibited phosphorylation of MET independently of downstream molecules. Further, 1 µM of foretinib or PD173074, a selective FGFR kinase inhibitor, inhibited phosphorylation of FGFR2 and downstream molecules, suggesting that foretinib targets FGFR2 in KATO-III. We confirmed this novel activity of foretinib against FGFR2 in OCUM-2M, another FGFR2-amplified gastric cancer cell line. Using a phospho-receptor tyrosine kinase array, we found that foretinib inhibits phosphorylation of epidermal growth factor receptor (EGFR), HER3 and FGFR3 via MET inhibition in MKN-45, and EGFR, HER3 and MET via FGFR2 inhibition in KATO-III. Knockdown of HER3 and FGFR3 in MKN-45 with siRNA resulted in the partial inhibition of cell signaling and cell growth. In conclusion, foretinib appears effective against gastric cancer cells harboring not only MET but also FGFR2 amplification, and exerts its inhibitory effects by blocking inter-RTK signaling networks with MET or FGFR2 at their core.

Left atrial extension of metastatic lung tumor via pulmonary vein: report on the first case of Ewing sarcoma.

Extension of metastatic lung tumors into the left atrium via pulmonary veins is rare. Here, we report the first case of Ewing sarcoma exhibiting such extension. A 31-year-old man with pulmonary metastasis from Ewing sarcoma presented with a mass in the left lung, extending to the left atrium through the left inferior pulmonary vein. As the patient was considered to be at risk of tumor embolism, the mass was excised surgically.

Formation of a stannylstannylene via intramolecular carbene addition of a transient stannaacetylene (RSn[triple bond, length as m-dash]CR').

Photolysis of diazomethylstannylene [, Me(3)SiC([double bond, length as m-dash]N(2))(Ar)Sn:, Ar = C(6)H(3)-2,6-Tip(2), Tip = C(6)H(2)-2,4,6-(i-Pr)(3)] afforded unusual stannylstannylene via intramolecular carbene addition to an aromatic pi bond of stannaacetylene ; the structures of compounds and were fully characterized by X-ray crystallography.

Structure determination of triplet diphenylcarbenes by in situ X-ray crystallographic analysis.

Crystalline-state photoreactions of the following diphenyldiazomethanes were investigated by in situ X-ray crystallography, spectroscopy, and theoretical calculations: bis(2,4,6-trichlorophenyl)diazomethane (1-N2), bis(2,4,6-tribromophenyl)diazomethane (2-N2), bis(2,6-dibromo-4-methylphenyl)diazomethane (3-N2), bis(2,6-dibromo-4-tert-butylphenyl)diazomethane (4-N2), (2,4,6-tribromophenyl)-(2,6-dimethyl-4-tert-butylphenyl)diazomethane (5-N2), bis(4-bromophenyl)diazomethane(6-N2), and diazofluorene (7-N2). Crystal structures of photoinduced triplet diphenylcarbenes (DPCs) of 1, 2, and 4 were determined. We found remarkable differences between their structural information obtained in the crystalline state and that previously obtained spectroscopically in a glass matrix. Although the triplet DPCs of 1, 2, and 4 have significantly different stabilities in solution, only subtle differences in their structural parameters, except for their C(:)-Ar bond lengths, are observed. It is noteworthy that the average bond length of C(:)-Ar for 4 (1.374 A) is considerably shorter than those for (3)1 and (3)2 (1.430 and 1.428 A, respectively), provided that the two C(:)-Ar bonds being compared were chemically equivalent. The most likely explanations for the small and large differences in bond lengths in 1, 2, and 4 may be derived from the packing effect. The packing patterns of 1 and 2 are identical, but that of 4 is totally different from those of 1 and 2. Moreover, these results are interpreted as indicating that triplet DPCs undergo relaxation upon softening of the environments. Theoretical calculations indicate that the potential energy surface of triplet DPCs in terms of the carbene angle is extremely flat and changes in the angles have little effect on the energies. Triplet DPCs with a sterically congested carbene center are trapped in a structure dictated by the precursor structure in a rigid matrix, even if this is not the thermodynamically most stable geometry, but undergo geometrical relaxation upon softening the matrix to relieve steric compression. ESR studies indicate that the interplanar angles are more flexible than the bond angles.

A dendrimer approach to high-spin polycarbenes. Conversion of connectivity from disjoint to non-disjoint by perturbation of nonbonding molecular orbital coefficients.

[structure: see text] Pentakis(diazo) compound was prepared by coupling 3,5-bis[4-[diazo(4-tert-butyl-2,6-dimethylphenyl)methyl]-3,5-dibromophenylethynyl]phenylacetylene with bis(4-iodo-2,6-dimethylphenyl)diazomethane under Sonogashira reaction conditions. Pentakis(carbene) generated by irradiation of the pentakis(diazo) compound was shown to have a high-spin state with S = 4.4 at 2.0 K.

Triplet diphenylcarbenes protected by trifluoromethyl and bromine groups. A triplet carbene surviving a day in solution at room temperature.

Two types of diphenyldiazomethanes having two trifluoromethyl and two bromine groups at the ortho positions, either in unsymmetrical or in symmetrical fashion, that is, (2,6-dibromo-4-phenylphenyl)[4-phenyl-2,6-bis(trifluoromethyl)phenyl]diazomethane (U-1-N2) and bis(2-bromo-4-phenyl-6-trifluoromethylphenyl)diazomethane (S-1-N2), are prepared. Triplet diphenylcarbenes (U-(3)1 or S-(3)1) are generated from those precursors and are characterized by ESR, UV/vis spectroscopy at low temperature, as well as time-resolved UV/vis spectroscopy at room temperature. Those carbenes are shown to be at least 2 orders of magnitude less reactive than the most stable triplet diphenylcarbene thus far known, that is, bis(2,6-dibromo-4-phenylphenyl)carbene. It has been also shown that S-(3)1 is significantly more stable than U-(3)1 even though both have the same two kinds of substituents. It is suspected that the perpendicular alignment of the two most bulky groups is a more effective way to shield the carbenic center than the planar one. By this way, triplet substituted diphenylcarbene surviving nearly a day in solution at room temperature is realized for the first time.

o-Phenylene halocarbenonitrenes and o-phenylene chlorocarbenocarbene: a combined experimental and computational approach.

[reaction: see text] Computations find that o-phenylene(halo)carbenonitrenes 2-XN, X = F, Cl, Br, have quinoidal singlet biradical ground states such as the parent o-phenylenecarbenonitrene (2-HN). Compared to the parent 2-HN, halogen substitution stabilizes the A'' states relative to the A' ones. Halogen substitution also affects the barrier and exothermicity of the ring-opening reaction (to form unsaturated nitriles 4-XN, X = F, Cl, Br), but it has a smaller effect on the ring-closing reaction (to form benzo(aza)cyclobutadiene 3-XN, X = F, Cl, Br). Attempts to generate and observe the o-phenylene(halo)carbenonitrenes 2-XN, X = F, Cl, Br, using matrix isolation spectroscopy under conditions similar to those of the successful observation of 2-HN failed. Instead, the observed photoproducts were a mixture of 3-XN and 4-XN. In each case, the major product of the mixture appears to be the thermodynamically more stable one. In the case of X = Br, the observed mixture contains an additional component that is postulated to be Z-6-BrN. o-Phenylenechlorocarbenocarbene is also computed to have a quinoidal singlet biradical ground state and relatively stabilized A'' excited states. Attempts to generate the biscarbene under matrix isolation conditions led to the detection of benzochlorocyclobutadiene (3-ClC), small amounts of the ring-open product (dienediyne 4-ClC), and cycloalkyne 5-ClC. Computations suggest that the formation of 5-ClC implies the generation of Z-6-ClC, which is analogous to the formation of Z-6-BrN from 2-BrN.