Immunopheotype of Gastrointestinal stromal tumours (GIST)

Histogenesis:
It has been suggested that GISTs originate from the interstitial cell of Cajal (ICC), or from a primitive stem cell that differentiates towards both the ICC and smooth muscle phenotye.

Sites:
GISTs occur at every level of the GI tract. Most tumours arise in the stomach (60%) and about
20–30% occur in the small intestine. Colorectal and oesophageal GISTs account for less than 10%. A small proportion of GISTs arise in extra-GI tract sites including the omentum, mesentery and retroperitoneum.

Morphologic patterns:
GISTs show a spectrum of histological features.Morphologically, the cells of GISTs are spindle, epithelioid, mixed pattern and occasionally pleomorphic.Spindle cell type is the predominant pattern, seen in 70% of GIST cases.

Immunophenotype
The overwhelming majority of GISTs express KIT protein (detected as CD117).The results of KIT immunostaining depend on several technical factors including fixation, tissue preparation, variations in antibody clones in terms of specificity and sensitivity, antibody dilutions and staining techniques. This may account, in part, for the reported immunophenotypic heterogeneity in GISTs. Recently, it has been emphasized that CD117should be performed without epitope retrieval.

Given the potential clinical importance of CD117 immunostaining, optimization of the staining techniques and reproducibility are critical. The pattern of staining is variable Diffuse strong cytoplasmic staining is the predominant pattern. Membranous staining and dot-like ‘golgi pattern’ staining can be identified. It has been suggested that different staining patterns correlate with different types of c-kit mutations. Stromal mast cells and ICC are useful internal positive controls to supplement the normal positive and negative controls.

Immunohistochemical detection of KIT does not necessarily imply c-kit activation. Indeed, CD117 is expressed by other tumour types such as melanoma and soft tissue sarcomas including dermatofibrosarcoma protuberans, synovial sarcoma and angiosarcomas. Therefore, CD117 immunoreactivity should be interpreted in the context of morphology and clinical setting.However, it is increasingly recognized that a high level of KIT expression is not characteristic for tumours with non-mutant KIT isoforms or tumours harbouring PDGFRA mutations.
CD34 is a transmembrane glycoprotein present on human haematopoietic progenitor cells and vascular endothelium. CD34 is detectable in approximately 70% of GISTs. The oesophageal and rectal GISTs have the highest frequency of CD34 positivity, whereas small intestinal tumours are the lowest percentage of CD34 positivity.

Actin expression is reported in approximately 30% of cases.Smooth muscle actin (SMA)expression is often reciprocal with CD34 expression: the SMA-positive tumours are often CD34 negative and vice versa. Some tumours may show a mosaic pattern with actin-positive and CD34-negative areas and vice versa.
Desmin-positive immunostaining is uncommon and, if present, is often limited to scattered tumour cells. Prominent staining is more common in epithelioid neoplasms. GISTs are generally negative for S100. Focal positive staining for cytokeratin markers can be seen especially in malignant epithelioid GISTs.

Proliferation markers (Ki-67, MIB-1 and proliferating cell nuclear antigen (PCNA)) may aid in tumour evaluation. It has been reported that tumours with more than 10% of nuclei that are positive for the KI-67 analogue are associated with metastases and poor survival rate.

In other studies, the MIB-1 index was not superior to mitotic count as a prognostic factor. Alterations of the tumour suppressor gene p16INK4A have been shown to be an independently poor prognostic factor.It has been previously regative p16 immunostaining is associated with malignant behaviour in GISTs.

GISTs with PDGFRA mutations are usually CD117 negative but may respond to STI-571; therefore, KIT detection may not be required for the treatment eligibility for Imatininb.



References:
1)Rubin BP, Fletcher JA, Fletcher CD. Molecular Insights into the histogenesis and pathogenesis of gastrointestinal stromal tumors. Int J Surg Pathol 2000;8:5–10.
2)Kindblom LG, Remotti HE, Aldenborg F, Meis-Kindblom JM.Gastrointestinal pacemaker cell tumor (GIPACT): gastrointestinal stromal tumors show phenotypic characteristics of the
interstitial cells of Cajal. Am J Pathol 1998;152:1259–69.
3) Miettinen M, Lasota J. Gastrointestinal stromal tumors—definition, clinical, histological, immunohistochemical, and molecular genetic features and differential diagnosis.
Virchows Arch 2001;438:1–12.
4)M.Sabah et al.Gastrointestinal stromal tumours: An update.Current Diagnostic Pathology (2005) 11, 400–410

Significance of Atypical Small Acinar Proliferation (ASAP) in Prostate needle biopsy

Many time while reporting prostate needle biopsy, we come across features, which are suspicious for malignancy, but hinder a definitive diagnosis of carcinoma, because of concern about over diagnosis. These are the cases, which are labelled as ASAP, -atypical small acinar proliferation.

Diagnostic criteria for ASAP :
For pathologists, 3 questions need to be answered before the diagnosis of cancer in a small lesion:
• Would you be absolutely confident of this biopsy diagnosis if it were followed by a negative radical prostatectomy?
• Would another colleague pathologist agree with the diagnosis of cancer?
• Can you confidently support the diagnosis of adenocarcinoma based solely on this biopsy?

If the answer to any of these questions is “No,” then use of the more conservative diagnosis of ASAP is recommended.

Reasons for the Diagnosis of ASAP are :

• Small number of acini in the focus of concern.
• Small focus size, average 0.4 mm in diameter.
• Loss of focus of concern in deeper levels.
• Distortion of acini raising concern for atrophy.
• Lack of convincing features of cancer (insufficient nucleomegaly or nucleolomegaly).
• Foamy cytoplasm raising concern for foamy gland carcinoma.
• Conflicting immunohistochemical findings.

Significance of ASAP. -

Prostate cancer is found in up to 60% of repeat biopsies after the diagnosis of ASAP. Thus
ASAP in a biopsy is a significant predictor for concurrent or subsequent cancer. The high predictive value of atypical small acinar proliferation (ASAP) for subsequent adenocarcinoma indicates a need for repeat biopsy.

References:

1. Borboroglu PG, Sur RL, Roberts JL, et al. Repeat biopsy strategy in patients with atypical small acinar proliferation or high grade prostatic intraepithelial neoplasia on initial prostate needle biopsy. J Urol. 2001;166:866–870.
2. Cheville JC, Reznicek MJ, Bostwick DG. The focus of “atypical glands,suspicious for malignancy” in prostatic needle biopsy specimens: incidence,histologic features, and clinical follow-up of cases diagnosed in a community practice. Am J Clin Pathol. 1997;108:633– 640.
3. Iczkowski KA, Bassler TJ, Schwob VS, et al. Diagnosis of “suspicious for malignancy” in prostate biopsies: predictive value for cancer. Urology.1998;51:749 –757; discussion 757–748.

4. Isabelle Meiers, at el. Atypical Small Acinar Proliferation in the prostate :Pathology Case reviews • Volume 13, Number 4, July/August 2008;13: 129–134

Sentinel Lymph Node Biopsy in Melanoma (SLNB)

Clinical Significance of Sentinel Lymph node in melanoma. :

SLNB is very accurate in predicting the status of the remaining regional lymph nodes.
It is currently the most significant independent prognostic indicator for survival when compared with all other factors, including tumour thickness and the presence of ulceration.

According to some studies, the relapse rate for H&E detected SLN positive patients is higher (up to 67%), whereas the relapse rate for SLN negative patients is low (2–6%) during the same period.

Indications for SLNB procedure :

1. Primary Melanoma with thickness greater than 1.0 mm,
   or
2. Primary Melanoma less than 1mm with Clark's level four or five or presence of ulceration.

Pathology Protocol:

The current standard for the diagnosis of SLN metastasis is based on routine H&E histology and immunohistochemistry (IHC).
I follow the Cochran Method.It is as follows:
1. The lymph node is either bivalved or cut into 3 mm blocks, depending on the size of the node.
2. Sections 1, 3, and 5 are stained with haematoxylin and eosin (H&E),
3. Sections 2 and 4 are immunohistochemically stained for S-100 and HMB-45.

The sensitivity of detection is increased with IHC, multiple sectioning and reverse transcriptase polymerase chain reaction (RT-PCR) techniques. The role of such molecular genetic techniques in identifying melanoma proteins remains undefined, despite greater sensitivity.

Caution.:
‘‘Surgeons should be aware that the subcapsular region is crucial in sentinel lymph node (SLN) evaluation and the architecture of the SLN can be disrupted easily if the procedure is not carried out with care.’’

To reduce the false negative rate, surgeons should avoid crushing and excessive cautery usage to preserve the integrity of the SLN. It is also important not to cut into the SLN and complete excision of the whole SLN is crucial.

False positive results. :
False positives resulting from,

1. Benign naevic cells raise concern and necessitate further refinement. Naevic cells are usually present within the capsule (intracapsular) or within the trabeculae, and typically stain negatively, or only faintly positively, with HMB-45.


2. Reactive dendritic cells, nerve fragments, and benign naevic cells may each stain positively for S100. HMB-45 stain allowed us to differentiate benign naevic cells from their malignant counterparts.
   Examination at the subcapsular level, combined with the use of S100 staining, is the most practical and sensitive method to ensure the detection of micrometastatic nodal disease.
   

References:
· Gershenwald JE, Thompson W, Mansfield PF, et al. Multi-institutional melanoma lymphatic mapping experience: the prognostic value of sentinel node status in 612 stage I or II melanoma patients. J Clin Oncol 1999;3:976–83.
· Balch CM, Buzaid AC, Atkins MB, et al. Final version of the American joint committee on cancer staging system for cutaneous melanoma. J Clin Oncol2001;19:3635–48.
· White RR, Stanley WE, Johnson JL, et al. Long-term survival in 2,505 patientswith melanoma with regional lymph node metastasis. Ann Surg 2002;235:879–87.
· McCready DR, Ghazarian DM, Hershkop MS, et al. Sentinel lymph-nodebiopsy after previous wide local excision for melanoma. Can J Surg 2001;44:432–4.
· Cochran AJ, Huang RR, Guo J, et al. Current practice and future directions inpathology and laboratory evaluation of the sentinel node. Ann Surg Oncol 2001;8(9S):13–17.
· Jansen L, Nieweg OE, Peterse JL, et al. Reliability of sentinel lymph node biopsy for staging melanoma. Br J Surg 2000;87:484–9.
· C A Murray, W L Leong, D R McCready and D M Ghazarian Histopathological patterns of melanoma metastases in sentinel lymph nodes J. Clin. Pathol. 2004;57;64-67