March 2011

Editor:
Fredrick L. Kiechle, MD, PhD

Q. Is there any way to prospectively detect ciguatoxin in marine species of fish to prevent the de-velopment of ciguatera—a disease for which there is no treatment, which in its extreme form can result in paralysis?

A. Ciguatera fish poisoning affects an estimated 25,000 people annually, mainly in tropical and subtropical Pacific and Indian Ocean insular regions and the tropical Caribbean, though other areas are not immune owing to the migration of fish. The term ciguatera comes from the Spanish common name given to the poisonous sea snail, Turbo pica, which causes poisoning symptoms similar to those of ciguatoxins. Today, humans are generally exposed to ciguatoxins when they ingest carnivorous fish that accumulate ciguatoxins through the food chain. Such fish feed on herbivorous fish, which feed on gambiertoxin-containing detritus, algae, or plants. These latter toxins get biotransformed into ciguatoxins in the herbivorous fish. The ciguatoxins are lipid-soluble polyethers containing 13 to 14 rings fused by ether linkages, forming a ladder-like structure. The ciguatoxins are further characterized as those found in Pacific Ocean fish (P-CTX) and those found in Caribbean fish (C-CTX), with the most potent or prominent ciguatoxin being CTX-1 (P-CTX-1 and C-CTX-1). These toxins are odorless and tasteless and withstand heating, salting, drying, smoking, and freezing, and thus they remain toxic after cooking. The mechanism of action of these toxins is to prolong the opening of sodium pores in muscle and nerve cells via activation of voltage-dependent sodium channels.

Signs and symptoms of ciguatoxin poisoning are highly variable but generally include gastrointestinal dis-turbances (watery diarrhea, nausea, vomiting, cramping) within 24 hours of ingestion followed by neurological deficits including paresthesias, numbness, and cold allodynia. Severe effects include hypotension, respiratory insufficiency, and bradycardia. These effects can last for months or longer. Fatalities are not common. Interestingly, ciguatoxins can be transmitted through sexual relations in which a poisoned partner transmits the toxins to an unaffected partner.

A number of testing protocols can be used to screen fish for ciguatoxins. Several bioassays are used, including the mouse, chicken, mongoose, and cat bioassays. The mouse bioassay is the most widely used. As with all bioassays, the findings must be interpreted carefully to differentiate clearly the effects of ciguatoxins from those of other potential toxins that might be present in extracts or tissues given to the animals. Nonvertebrate bioassays also exist, for example, brine shrimp, mosquito, and dipteral larvae. Sodium-channel-binding in vitro assays are available for testing purposes. With respect to biochemical assays, cytotoxicity and immunoassays (radioimmunoassay, ELISA, stick test) have been developed but can lack specificity due to cross-reactivities. Chemical assays include liquid chromatography with fluorescence detection and liquid chromatography-mass spectrometry. However, these assays are challenging, especially the isolation of the ciguatoxins from the fish flesh. Recently, a “rapid” extraction of fish flesh homogenate for ciguatoxins, specifically P-CTX-1, was reported using LC-MS/MS as the analytical finish. The method was able to detect P-CTX-1 at 0.1 ppb, consistent with that expected (0.1–5 ppb) in the flesh of carnivorous Pacific fish containing this ciguatoxin.

Bibliography

Robert A. Middleberg, PhD
NMS Labs
Willow Grove, Pa.

Former consultant, CAP Toxicology
Resource Committee

Q. In staging breast carcinoma, the CAP cancer protocol for T4 says “direct extension to the chest wall and/or to the skin (ulceration or skin nodules). Note: invasion of the dermis alone does not qualify as pT4.” However, T4b specifies “satellite nodules.” If a tumor creates a skin nodule (palpable mass) by direct extension without a satellite nodule, edema, ulceration, or evidence of inflammatory carcinoma, should it be classified as T4, T4b, or T1-3 as determined by size?

A. The first edition of the American Joint Committee on Cancer’s Cancer Staging Manual described the criteria for classification of breast cancers as T4, and essentially the same wording is used in the seventh edition.¹ At the time of the first edition in 1977, the majority of women presented with palpable cancers and many had locally advanced disease. Grave prognostic indicators were clinically evident invasion into the skin with ulceration, edema of the skin, satellite skin nodules, invasion into the chest wall beyond the pectoralis muscle, and signs of inflammatory carcinoma.² Satellite skin nodules (to distinguish skin involvement in the general area of the carcinoma from distant metastatic disease) were described by C.D. Haagensen, MD, as “a local manifestation of the disease in the breast,” and he wrote that they “result from extension of the disease along lymphatics, or ducts or fascial strands, which lead the carcinoma into contact with the skin at some little distance from the primary focus.”²

Thankfully, breast cancers are now generally detected at smaller sizes and the “grave prognostic indicators” are uncommon findings. When satellite skin nodules are present, they are generally the result of lymphovascular invasion in the dermis. Thus, they are a form of intramammary metastasis and this underlying biology correlates with the poor prognostic significance of this finding.

The CAP cancer protocol uses the same wording as the current seventh edition of the AJCC Cancer Staging Manual. Under the general description of T4, the term “skin nodule” is used. Under the description of T4b, the term “satellite nodules” is specified. Only the presence of a clinically evident satellite skin nodule should result in classification as T4b.

Therefore, the cancer in question with direct skin invasion would be classified according to size, as the cancer is not associated with ulceration and would not be considered a satellite skin nodule. Studies have shown that cancers with direct skin invasion without ulceration are more likely to be associated with lymph node metastases, but this finding does not have a large impact on prognosis for node-negative women.^3,4

References

Susan Lester, MD, PhD
Brigham and Women’s Hospital
Boston

Member, CAP Cancer Committee

Yunn-Yi Chen, MD, PhD
UCSF Medical Center
San Francisco