Pattern of Residual Submucosal Involvement after Neoadjuvant Therapy for Rectal Cancer: A Rationale for the Utility of Endoscopic Submucosal Resection.

Background and Objectives: Full-thickness trans anal local excision for tumors with favorable response following neoadjuvant therapy for locally advanced rectal cancer (LARC) is a common strategy for organ preservation, but it could be associated with a high rate of postoperative complications. We describe the incidence and pattern of submucosal involvement in surgical specimens following neoadjuvant therapy for LARC and whether limiting local excision of the residual tumor bed to only mucosal/submucosal layers of the rectal wall is sufficient for accurately predicting the ypT status of residual cancer, providing a pathological rationale to replace full-thickness local excision by endoscopic submucosal resection. Materials and Methods: This was a single-institution retrospective study conducted at a teaching community hospital. We reviewed clinical and pathological findings with slides of 82 patients diagnosed with LARC treated at our center between 2006 and 2020. Eligibility criteria mirrored our current organ preservation trials. Results: No tumor was found in surgical specimens in 28 cases (34%). Additionally, 4, 22, 27, and 1 cases were staged as ypT1, ypT2, ypT3, and ypT4, respectively. Residual malignant cells were found in the submucosal layer in 98% of cases with ypT+ stage, with 'skip lesions' in only 2% of cases. Conclusions: A very high incidence of submucosal involvement is noticed in residual tumors after neoadjuvant therapy, providing pathological rationale to study the role of endoscopic submucosal resection as a restaging tool for tumors with favorable response after neoadjuvant therapy when organ preservation strategy is pursued. This study was limited by its retrospective design and relatively small number of patients.

Practical diagnostic utility of thyroid fine-needle aspiration cell blocks: is always too much?

INTRODUCTION: Thyroid fine-needle aspiration (tFNA) is a powerful screening tool for assessing solitary thyroid nodules. Generally, morphologic evaluation of smears yields an accurate diagnosis; but, in some cases it is useful to have a cell block (CB) to conduct ancillary studies such as immunohistochemistry (IHC). Cytologic diagnoses guide clinical decisions, so it is important that accurate and efficient diagnoses be rendered. Our study evaluates the diagnostic utility of the CB in the evaluation of tFNAs. MATERIALS AND METHODS: We performed a retrospective chart review of all tFNA specimens from January 2014 to July 2019. Data collected included TAT (in days), diagnosis, if a CB was prepared, and if it was diagnostically contributory. Descriptive statistics were calculated. Data were analyzed using the χ2 test and the Mann-Whitney U-test. RESULTS: Of the 2321 specimens, 40.2% (933) had CB and only 0.3% (7) were diagnostically contributory. IHC was used for 2 cases. For cases with CB, the median TAT was one day [0-18 days] and the median TAT without CB was 0 [0-9 days]. There was a significant difference in TAT between cases with a CB and those without. Most cases without a CB had same-day TAT (66.4%), whereas only 1.1% of those with a CB had same day TAT. Cases with CB were more likely to have a TAT >1 day (65% versus 12.1%) or >3 days (25.4% versus 10%) than those without a CB (P < 0.0001). CONCLUSIONS: We found the diagnostic utility of CB for tFNAs to be very low. The addition of a CB added at least 1 day to the TAT in all diagnostic strata. The additional time causes patients to wait for results, even for nondiagnostic studies. The increased TAT, resources, and manpower use may be reduced if CB were produced only as needed-if the results of the smear were ambiguous or if ancillary tests were needed to confirm the diagnosis.

Codon-specific effects of tRNA anticodon loop modifications on translational misreading errors in the yeast Saccharomyces cerevisiae.

Protein synthesis requires both high speed and accuracy to ensure a healthy cellular environment. Estimates of errors during protein synthesis in Saccharomyces cerevisiae have varied from 10-3 to 10-4 errors per codon. Here, we show that errors made by ${\rm{tRNA}}^{\rm Glu}_{\rm UUC}$ in yeast can vary 100-fold, from 10-6 to 10-4 errors per codon. The most frequent errors require a G•U mismatch at the second position for the near cognate codon GGA (Gly). We also show, contrary to our previous results, that yeast tRNAs can make errors involving mismatches at the wobble position but with low efficiency. We have also assessed the effect on misreading frequency of post-transcriptional modifications of tRNAs, which are known to regulate cognate codon decoding in yeast. We tested the roles of mcm5s2U34 and t6A37 and show that their effects depend on details of the codon anticodon interaction including the position of the modification with respect to the base mismatch and the nature of that mismatch. Both mcm5 and s2 modification of wobble uridine strongly stabilizes G2•U35 mismatches when ${\rm{tRNA}}^{\rm Glu}_{\rm UUC}$ misreads the GGA Gly codon but has weaker effects on other mismatches. By contrast, t6A37 destabilizes U1•U36 mismatches when ${\rm{tRNA}}^{\rm Lys}_{\rm UUU}$ misreads UAA or UAG but stabilizes mismatches at the second and wobble positions.

Effects of tRNA modification on translational accuracy depend on intrinsic codon-anticodon strength.

Cellular health and growth requires protein synthesis to be both efficient to ensure sufficient production, and accurate to avoid producing defective or unstable proteins. The background of misreading error frequency by individual tRNAs is as low as 2 × 10(-6) per codon but is codon-specific with some error frequencies above 10(-3) per codon. Here we test the effect on error frequency of blocking post-transcriptional modifications of the anticodon loops of four tRNAs in Escherichia coli. We find two types of responses to removing modification. Blocking modification of tRNA(UUC)(Glu) and tRNA(QUC)(Asp) increases errors, suggesting that the modifications act at least in part to maintain accuracy. Blocking even identical modifications of tRNA(UUU)(Lys) and tRNA(QUA)(Tyr) has the opposite effect of decreasing errors. One explanation could be that the modifications play opposite roles in modulating misreading by the two classes of tRNAs. Given available evidence that modifications help preorder the anticodon to allow it to recognize the codons, however, the simpler explanation is that unmodified 'weak' tRNAs decode too inefficiently to compete against cognate tRNAs that normally decode target codons, which would reduce the frequency of misreading.

Mutations of ribosomal protein S5 suppress a defect in late-30S ribosomal subunit biogenesis caused by lack of the RbfA biogenesis factor.

The in vivo assembly of ribosomal subunits requires assistance by maturation proteins that are not part of mature ribosomes. One such protein, RbfA, associates with the 30S ribosomal subunits. Loss of RbfA causes cold sensitivity and defects of the 30S subunit biogenesis and its overexpression partially suppresses the dominant cold sensitivity caused by a C23U mutation in the central pseudoknot of 16S rRNA, a structure essential for ribosome function. We have isolated suppressor mutations that restore partially the growth of an RbfA-lacking strain. Most of the strongest suppressor mutations alter one out of three distinct positions in the carboxy-terminal domain of ribosomal protein S5 (S5) in direct contact with helix 1 and helix 2 of the central pseudoknot. Their effect is to increase the translational capacity of the RbfA-lacking strain as evidenced by an increase in polysomes in the suppressed strains. Overexpression of RimP, a protein factor that along with RbfA regulates formation of the ribosome's central pseudoknot, was lethal to the RbfA-lacking strain but not to a wild-type strain and this lethality was suppressed by the alterations in S5. The S5 mutants alter translational fidelity but these changes do not explain consistently their effect on the RbfA-lacking strain. Our genetic results support a role for the region of S5 modified in the suppressors in the formation of the central pseudoknot in 16S rRNA.