The expression of TTF1, CDX2 and ISL1 in 74 poorly differentiated neuroendocrine carcinomas.

BACKGROUND: The expression profile of immunohistochemical markers of origin in poorly differentiated neuroendocrine carcinoma (PDNEC) is not well studied. MATERIALS AND METHODS: Seventy-four PDNECs from gastroenteropancreatic (GEP) organs and the lung, including 48 large cell NEC (LCNEC) and 26 small cell carcinomas (SmCC), were subject to immunohistochemical staining for CDX2, TTF1 and ISL1. The staining intensity (1 to 3) and percentage of positive tumor cells [0 (negative), 1 (<50%) and 2 (≥50%)] were assessed. The multiplicative index (maximum 6) was calculated and the average total score (aTS) was determined for each primary site and histologic subtype. RESULTS: In the 38 GEP and 36 lung PDNECs, CDX2, TTF1 and ISL1 staining was observed in 71% (aTS 2.8), 16% (aTS 0.4), 63% (aTS 1.9), and 22% (aTS 0.6), 72% (aTS 2.9) and 92% (aTS 3.8), respectively. GEP PDNECs showed a higher aTS for CDX2 and lower aTS for TTF1 and ISL1, compared to that of lung PDNECs (Student's t-test, p < 0.001). SmCC had a higher aTS for TTF1 and ISL1 (p < 0.001) and lower aTS for CDX2 (p < 0.002) than that of LCNEC. CONCLUSIONS: CDX2 and TTF1 demonstrate potential utility in suggesting the primary site of PDNEC. In addition, CDX2 may be useful in supporting the diagnosis of LCNEC in cases with overlapping or borderline morphology. Utility of ISL1 as an adjunctive diagnostic marker of SmCC remains to be studied.

Pure Discrete Punctate Nuclear Staining Pattern for MLH1 Protein Does Not Represent Intact Nuclear Expression.

Immunohistochemical staining for DNA mismatch repair (MMR) proteins is commonly used to screen for Lynch syndrome. Several laboratories have noticed a discrete punctate nuclear staining pattern for MLH1 that caused confusion in interpretation. This study was designed to investigate whether this particular staining pattern represents intact nuclear expression of MLH1. MMR proteins immunostaining and follow-up testing in 161 consecutive colorectal adenocarcinoma cases (86 biopsies, 75 resections) were retrospectively reviewed. Both discrete punctate nuclear staining and diffuse nuclear staining patterns for MLH1 were observed in internal control cells in 76 biopsies and 27 resections. Only diffuse nuclear staining was seen in the remaining 10 biopsies and 48 resections (P < .0001). Pure discrete punctate nuclear staining pattern for MLH1 was observed in 11 tumors (9 biopsies, 2 resections), and completely negative staining was seen in 13 tumors (2 biopsies, 11 resections; P = .003). Those 24 tumors (21 patients) invariably showed loss of PMS2. Three patients whose biopsies showed pure punctate staining for MLH1 underwent repeat testing on resections: 1 retained the punctate staining and 2 showed complete loss of MLH1. Nine patients who showed loss of PMS2 and pure punctate MLH1 staining underwent molecular testing: 4 had BRAF V600E mutations and 1 had MLH1 gene mutation. Our data showed that discrete punctate nuclear staining for MLH1 is more commonly seen in biopsy specimens. Pure discrete punctate staining pattern is paired with loss of PMS2 expression and may be associated with BRAF or MLH1 gene mutation, thus it should not be interpreted as intact nuclear expression.

The "Rosen Triad": tubular carcinoma, lobular carcinoma in situ, and columnar cell lesions.

The histologic triad of tubular carcinoma (TC), columnar cell lesion (CCL), and lobular carcinoma in situ (LCIS) has been recognized, but has not yet been fully characterized. The "Rosen Triad"-named in tribute to its first categorical description by the eponymous pathologist-is a morphologic observation that may have important clinical and pathologic implications. To study these implications, the literature on the topic was reviewed. Our own institution's experience with this triad was also reviewed via a study of clinicopathologic material from all TCs diagnosed at excision during a 5-year period (2001 to 2006). The diagnosis of TC was confirmed in 86 of our cases, and relevant patient data were analyzed. TC was associated with some degree of CCL in all (100%, 86/86) cases and with LCIS in 53% (46/86) of cases. Although cases of TC that were associated with LCIS (vs. those not associated with LCIS) seemed to be slightly more likely to have multifocal TC, have another synchronous higher-grade invasive carcinoma and show nodal positivity, these differences were not found to be statistically significant (P<0.05). All 3 lesions (TC, CCL, and LCIS), whenever tested, were estrogen receptor positive, progesterone receptor-positive, and Her-2/neu negative. On the basis of our review of the literature and our own experience, until such time as the biologic explanation and clinical implication of this triad is further elucidated, we recommend that pathologists be aware of this triad and should proactively seek the other 2 lesions if any one of these elements of this triad is identified in any diagnostic breast tissue.

Microscopic ileitis in diverted and nondiverted enteric segments: an underrecognized condition with a multifactorial etiology.

Microscopic ileitis has been infrequently reported in the literature with the few reported cases usually associated with concurrent microscopic colitis. Having encountered a case of collagenous ileitis involving the diverted distal limb of a loop ileostomy and sparing the proximal limb, we examined additional cases of loop ileostomy, end ileostomy, colostomy, and the accompanying diverted colorectal segment for features of microscopic ileitis and colitis. A total of 101 cases of diverted and nondiverted enteric segments were examined from 37 loop ileostomies, 16 end ileostomies, and 12 colostomies status post-Hartmann's procedure. The patients' clinical histories, including demographics and risk factors for microscopic colitis, were obtained from electronic medical records. The index case and an additional case showed collagenous ileitis: the former in the diverted distal limb, and the latter in the nondiverted proximal limb of the loop ileostomy. The latter was associated with high ileostomy output with watery diarrhea. Two additional cases showed lymphocytic ileitis: one in the nondiverted proximal limb of loop ileostomy and the other in the end ileostomy. All 4 patients had one or more risk factors for microscopic colitis. The etiology of microscopic ileitis seems to be multifactorial, and microscopic ileitis may be underdiagnosed. The diverted enteric segment may be involved by microscopic enteritis, suggesting that additional factors other than fecal stasis and altered bacterial flora may be contributing to its pathogenesis. When microscopic ileitis is encountered, identifying associated risk factors, recognizing incipient clinical symptoms of microscopic colitis, and considering other associated diseases or conditions are warranted.