[Rich66]

from the xtend life brand site above:

Molecular distillation is the only process that can effectively remove metals, PCBs and other harmful toxins to a level that is perfectly safe for human consumption.

Better fish oil supplement manufacturers use ethanol (food grade) which does not leave residual component.

Ok..so molecular filtering good, molecular filtering with ethanol (fill 'er up) possibly better than hexanes.
What I still wonder about is whether a process designed to remove toxins and metals removes the pifas in question...i.e. the half empty interpretation of Dr. Block's half full statement "It is quite possible that there are no PIFAs in molecularly distilled fish oils". Ok..maybe..maybe not.

Having looked at a number of fish oil/cancer abstracts, I get the sense that DHA is the most potent component of this fishy oil. There are DHA only supplements available. Could it be that DHA isolated supplements have been further filtered/isolated and more "likely" to have had the offending pifas removed? Maybe..maybe not.

I asked Nature's Bounty brand about molecular filtering and independent testing and they responded in depth about testing without mentioning filtering. I rebounded the filtering question back to them..we'll see. Of course, I didn't ask what kind of molecular filtering it is. Oy. Maybe it's better to ask specifically about presence of the pifas, identified in this late arrival, but more detailed medscape article:
http://www.medscape.com/viewarticle/750026

The fatty acids were identified as polyunsaturated fatty acids (PIFAs), 12-oxo-5,8,10-heptadecatrienoic acid (KHT), and hexadeca-4,7,10,13-tetraenoic acid [16:4(n-3)]. In minute amounts, these fatty acids were able to induce resistance.

"The resistance is due to these two specific PIFAs," Dr. Daenen told Medscape Medical News. "EPA and DHA [eicosapentaenoic acid and docosahexaenoic acid] were used as controls and, importantly, did not induce resistance in our mouse models."
"Therefore, there is no need to avoid these fatty acids, or products containing these fatty acids, even in high doses," she added.

"The conditioned media contain a mixture of fatty acids, and these products are capable of inducing resistance to various chemotherapy agents," said Dr. Chabner, a professor of medicine at Harvard Medical School and director of clinical research, Massachusetts General Hospital Cancer Center, Boston. "These studies are done in mice with relatively high doses of drug, and have uncertain but potential applicability to clinical chemotherapy."

In a mouse model, they noted that both intravenous and subcutaneous injections of MSCs induced resistance to cisplatin. Interestingly, in vivo resistance was induced by MSCs not only for cisplatin but for oxaliplatin (10 mg/kg) and carboplatin (100 mg/kg), but not with 5-fluoroucil (100 mg/kg) or irinotecan (100 mg/kg).

to validate the findings in patients with cancer, levels of MSCs were measured in the whole blood of 50 patients with different types of tumors. The authors found a significant increase in MSC counts in the peripheral blood of patients with metastatic disease compared with those who had undergone a radical resection of the tumor and had no residual disease. These results indicated that MSCs are present in the circulation and will subsequently be exposed to chemotherapy. Also, the authors note that the number of circulating MSCs was similar to the number of MSCs sufficient to confer chemoresistance in mouse models.

But all the minutia and stone turning may be unnecessary if positive animal and human studies were done with relatively standard fish oil. It would be great if the brands or characteristics of the previously positive result fish oil were revealed.